43.1A: Methods of Reproducing - Biology

43.1A: Methods of Reproducing - Biology

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Animal reproduction is essential to the survival of a species; it can occur through either asexual or sexual means.

Learning Objectives

  • Describe reproduction in animals

Key Points

  • Reproduction (or procreation) is the biological process by which new “offspring” are produced from their “parents”.
  • Asexual reproduction yields genetically-identical organisms because an individual reproduces without another.
  • In sexual reproduction, the genetic material of two individuals from the same species combines to produce genetically-different offspring; this ensures mixing of the gene pool of the species.
  • Organisms that reproduce through asexual reproduction tend to grow exponentially and rely on mutations for DNA variation, while those that reproduce sexually yield a smaller number of offspring, but have larger genetic variation.

Key Terms

  • reproduction: the act of producing new individuals biologically
  • clone: a living organism produced asexually from a single ancestor, to which it is genetically identical

Animal Reproduction

Reproduction (or procreation) is the biological process by which new “offspring” (individual organisms) are produced from their “parents. ” It is a fundamental feature of all known life that each individual organism exists as the result of reproduction. Most importantly, reproduction is necessary for the survival of a species. The known methods of reproduction are broadly grouped into two main types: sexual and asexual.

In asexual reproduction, an individual can reproduce without involvement with another individual of that species. The division of a bacterial cell into two daughter cells is an example of asexual reproduction. This type of reproduction produces genetically-identical organisms (clones), whereas in sexual reproduction, the genetic material of two individuals combines to produce offspring that are genetically different from their parents.

During sexual reproduction, the male gamete (sperm) may be placed inside the female’s body for internal fertilization, or the sperm and eggs may be released into the environment for external fertilization. Humans provide an example of the former, while seahorses provide an example of the latter. Following a mating dance, the female seahorse lays eggs in the male seahorse’s abdominal brood pouch where they are fertilized. The eggs hatch and the offspring develop in the pouch for several weeks.

Asexual versus Sexual Reproduction

Organisms that reproduce through asexual reproduction tend to grow in number exponentially. However, because they rely on mutation for variations in their DNA, all members of the species have similar vulnerabilities. Organisms that reproduce sexually yield a smaller number of offspring, but the large amount of variation in their genes makes them less susceptible to disease.

Many organisms can reproduce sexually as well as asexually. Aphids, slime molds, sea anemones, and some species of starfish are examples of animal species with this ability. When environmental factors are favorable, asexual reproduction is employed to exploit suitable conditions for survival, such as an abundant food supply, adequate shelter, favorable climate, disease, optimum pH, or a proper mix of other lifestyle requirements. Populations of these organisms increase exponentially via asexual reproductive strategies to take full advantage of the rich supply resources. When food sources have been depleted, the climate becomes hostile, or individual survival is jeopardized by some other adverse change in living conditions, these organisms switch to sexual forms of reproduction.

Sexual reproduction ensures a mixing of the gene pool of the species. The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur. In addition, sexual reproduction usually results in the formation of a life stage that is able to endure the conditions that threaten the offspring of an asexual parent. Thus, seeds, spores, eggs, pupae, cysts, or other “over-wintering” stages of sexual reproduction ensure the survival during unfavorable times as the organism can “wait out” adverse situations until a swing back to suitability occurs.

3 Types of Reproduction that are Found in Lichens | Biology

On maturity the older portions of the thalli of lichens die and decay. The thallus breaks into pieces accidentally and each piece develops into a new plant. This occurs more frequently in pendant thallus, such as of Ramalina reticulata.

2. Isidia and soredia:

As described above (c and d), the vegetative reproduction takes place by means of isidia and soredia as they detach from the mother thalli.

B. Asexual spores:

Hyphae of few lichens break up into oidia, they germinate into new fungal hyphae and each oidium produces a lichen when comes in contact with suitable alga. Many lichens produce large number of small spore-like structures, pycniospores, within flask shaped pycnia, immersed within the thallus. These structures when act as male gametes are known as spermatia and spermagonia respectively.

C. Sexual reproduction:

In Ascolichens the fungus belongs to Ascomycetes and the sexual reproduction results in the formation of apothecia or perithecia. These fruiting bodies are small cup-like or disc-like and may be embedded in, or raised above the surface of thallus by short or long stalks. The structure of the wall of an apothecium is similar to that of the thallus it consists of an upper and a lower cortical layer with medulla, in between. Algal components may not be present in the vegetative part of the apothecium.

The bottom of the cup or the surface of the disc is the fertile part of the apothecium and is lined by the hymenium. Hymenium consists of asci and paraphyses growing vertically. Paraphyses contain a reddish oily substance in them and never project beyond asci. Each ascus contains eight ascospores, which become two celled prior to dissemination. Asci are the resultants of sexual union.

The female reproductive organ is an ascogonium (carpogonium) which develops from hypha deep in the algal layer. It is a long multicellular hypha, the coiled base of it is the oogonium and the straight portion above it the trichogyne. The trichogyne in some species projects beyond thallus. More than one ascogonia may develop at a point where an apothecium is later formed but only one becomes fertile.

The male reproductive body is spermagonium (pycnium). It is flask-shaped cavity immersed in the thallus and opens to the exterior by small ostiole. The fertile hyphae lining the inner surface of the spermagonium produce large number of small non-motile gametes spermatia. The spermatia are functional male gametes.

The spermatia are lodged against the sticky protruding tips of trichogynes, and the fact that ascogonia of thalli lacking spermagonia rarely produce ascocarps. In Collemodes bachmannianum a gelatinous lichen trichogyne does not protrude, but grows more or less horizontally in the thallus. Spermatia are borne laterally and terminally on surface of the hyphae with the thallus.

The growing trichogyne comes in contact with spermatia. The walls of contact dissolve and the male nucleus gradually passes downward to the oogonium, where it fuses with the female nucleus of the egg and the fertilization is effected.

Numerous branched, septate ascogenous hyphae containing one, two or many nuclei developed from the oogonium. The ultimate or the penultimate cells of the ascogenous hyphae develop into asci. At the same time sterile hyphae develop from below the ascogonium and the wall of the ascocarp. As the ascocarp grows it breaks through the thallus and appears, above the surface as a cup or disc or remains embedded.

The development of asci and ascospores resembles to that of typical Ascomycetes. Spores are shed only during moist weather on germination, a spore produces a germ tube which grows in all directions, and as soon as it comes in contact with a suitable alga, additional branches are formed to engulf the alga. Combined growth of the fungus and the alga continues and results in a lichen. In absence of a suitable alga the germ tube dies.

Basidiolichens reproduce by basidiospores produced on basidia as in typical Basidiomycetes. Lower surface of the thallus bears subhymenium, and basidia are arranged palisade-like on the lowermost face of each subhymenium. Each basidium bears four basidiospores at the tips of sterigmata.

Reproduction in Algae: 3 Modes

The following points highlight the three modes of reproduction in algae. The modes are: 1. Vegetative 2. Asexual 3. Sexual .

Mode # 1. Vegetative Reproduction:

In this type, any vegetative part of the thallus develops into new individual. It does not involve any spore formation and there is no alternation of generations. It is the most common method of reproduction in algae.

The vege­tative reproduction in algae is of the follow­ing types:

a. Cell division or fission:

It is the simplest method of reproduction. The unicellular forms of algae commonly reproduce by this simple process, often called binary fission as found in Chlamydomonas, Synechococcus (Fig. 3.16A), diatoms etc. In this method the vegetative cell divides mitotically into two daughter cells, those finally behave as new indi­vidual.

In this method, the multicellular filamentous thallus breaks into many-celled fragments, each of which gives rise to a new individual. The fragmentation may be accidental or by the formation of separation discs or by some other mechanical force or injury. It is found in Spirogyra, Ulothrix, Oedo- gonium, Zygnema, Cylindospermum (Fig. 3.16B) etc.

This method of vegetative reproduction is found in blue-green algae. The trichomes of blue-green algae break up within the sheath into many-celled segments called hormogo­nia or hormogones. They remain delim­ited by the formation of heterocysts, separation discs or necridia or by the death and decay of intercalary cells of the trichome. Hormogonia are com­monly found in Nostoc, Oscillatoria, Cylindosporium etc.

d. Formation of Adventitious Branches:

Adventitious branches are formed in different large thalloid algae, which, when detached from the plant body, develop into new individuals (e.g., Fucus, Dictyota). Protonema-like adventitious branches are formed from the internodes of Chara, stolons of Cladophora glomareta etc.

Tuber-like outgrowths are deve­loped due to storage of food at the tip of rhizoids and on the lower nodes of Chara, called bulbils (Fig. 3.16C). After detachment from the plant body, bulbils grow into new plants.

Star-shaped aggregation of starch containing cells develops on the lower nodes of Chara. These struc­tures are called amylum stars (Fig. 3.16D). When detached from the plant body, they grow into new plants.

In Protosiphon bud-like struc­tures are formed due to proliferation of vesicles delimited from the parental body by a septum, which, after detach­ment, grow into a new plant.

Mode # 2. Asexual Reproduction:

Asexual reproduction involves the formation of certain type of spores — either naked or newly walled. It is a process of rejuvenation of the protoplast without any sexual fusion. Each and every spore germinates into a new plant. In this method, there is no alternation of genera­tions.

The asexual spores may be of various types:

a. Zoospores:

These are motile naked spores provided with two, four or many flagella and called as bi-, quadri- or multiflagellate zoospores, respectively. Biflagellate zoospores are found in Chlamydomonas, Ulothrix (Fig. 3.17A) Ectocarpus etc., quadriflagellate zoos­pores are found in Ulothrix (Fig. 3.17B) and multiflagellate zoospores are found in Oedogonium (Fig. 3.17C).

But the multinucleate and multiflagellate zoospores as found in Vaucheria (Fig. 3.17D) are called synzoospores. Each zoospore has a chloroplast and an eye spot. The zoospores may be either haploid or diploid.

They are formed within the zoosporangium. There may be sin­gle zoospore (e.g., Oedogonium) or many zoospores (e.g., Cladophora) per zoosporangium. Zoospores are either haploid or diploid depending on the nature of plant body, gametophytic or sporophytic on which it develops.

The zoospores are liberated either by the disintegration of the zoosporangial wall or by the formation of an apical pore on the zoosporangium. After liberation the zoospores swim for a while, then with­draw their flagella, encyst and ulti­mately germinate into new plants.

Aplanospores are non- motile spores. These spores are formed either singly or its protoplast may divide to form many aplanospores inside spo­rangium during unfavourable conditions, especially in drought (e.g., Ulothrix (f ig. 3.17E), Microspora). The aplanospores may also be formed in certain algae of semiaquatic habitat.

When they appear identical to the parent cell, they are referred to as autospores (e.g., Scenedesmus, Chlorella etc.). Aplanospores with thickened wall and abundant food reserve are known as hypnospores (e.g., Pediastram, Sphaerella etc.).

They are formed to overcome prolonged period of desiccation. With the onset of favourable condition the hypnospores either directly germinate into a new individual or their protoplasts may form zoospores. Due to deposition of haematochrome pigment in their walls, the hypnospores of Chlamydomonas nivalis are red in colour.

Diploid plants of some algae (e.g., Polysiphonia, Fig. 3.17F) pro­duce a special type of haploid aplano­spores, called tetraspores, formed within tetrasporangium. The diploid nucleus of a tetrasporangium divides meiotically to form four haploid nuclei which — with little amount of protoplasm — are deve­loped into four tetraspores. After libe­ration the tetraspores germinate to form male and female gametophytes.

The vegetative cells of certain filamentous algae develop into elonga­ted thick-walled spore-like structures with abundant food reserves, called akinetes (e.g., Gloeotrichia, Fig. 3.17G). They can tide over the unfavourable conditions. With the onset of favourable condition they germinate into new indi­viduals.

In some algae, spores are regularly cut off at the exposed distal end of the protoplast in basipetal succession, called exospores. These spores aggregate in groups and develop new colonies, e.g., Chamaesiphon (Fig. 3.17H).

These are small spores formed by the divisions of the mother protoplast. They are also called conidia or gonidia. They are set free after the dissolution of mother wail. Without taking rest, the spores germinate direct­ly and develop into a new plant, e.g., Dermocarpa (Fig. 3.17 I).

Mode # 3. Sexual Reproduction:

All algae except the members of the class Cyanophyceae reproduce sexually. During sexual reproduction gametes fuse to form zygote (Fig. 3.18). The new genetic set up can develop by the fusion of gametes coming from the different parents.

Depending on the structure, physio­logical behaviour and complexity of sex organs, sexual reproductions are of the following five types:

Meiosis – Sexual Reproduction

The ability to reproduce in kind is a basic characteristic of all living things. In kind means that the offspring of any organism closely resembles its parent or parents. Hippopotamuses give birth to hippopotamus calves Monterey pine trees produce seeds from which Monterey pine seedlings emerge and adult flamingos lay eggs that hatch into flamingo chicks. In kind does not generally mean exactly the same. While many single-celled organisms and a few multicellular organisms can produce genetically identical clones of themselves through mitotic cell division, many single-celled organisms and most multicellular organisms reproduce regularly using another method.

Figure 1: Each of us, like these other large multicellular organisms, begins life as a fertilized egg. After trillions of cell divisions, each of us develops into a complex, multicellular organism. (credit a: modification of work by Frank Wouters credit b: modification of work by Ken Cole, USGS credit c: modification of work by Martin Pettitt)

Sexual reproduction is the production by parents of sex cells and the fusion of two sex cells to form a single, unique cell. In multicellular organisms, this new cell will then undergo mitotic cell divisions to develop into an adult organism. A type of cell division called meiosis leads to the cells that are part of the sexual reproductive cycle. Sexual reproduction, specifically meiosis and fertilization, introduces variation into offspring that may account for the evolutionary success of sexual reproduction. The vast majority of eukaryotic organisms can or must employ some form of meiosis and fertilization to reproduce.

Sexual reproduction was an early evolutionary innovation after the appearance of eukaryotic cells. The fact that most eukaryotes reproduce sexually is evidence of its evolutionary success. In many animals, it is the only mode of reproduction. And yet, scientists recognize some real disadvantages to sexual reproduction. On the surface, offspring that are genetically identical to the parent may appear to be more advantageous. If the parent organism is successfully occupying a habitat, offspring with the same traits would be similarly successful. There is also the obvious benefit to an organism that can produce offspring by asexual budding, fragmentation, or asexual eggs. These methods of reproduction do not require another organism of the opposite sex. There is no need to expend energy finding or attracting a mate. That energy can be spent on producing more offspring. Indeed, some organisms that lead a solitary lifestyle have retained the ability to reproduce asexually. In addition, asexual populations only have female individuals, so every individual is capable of reproduction. In contrast, the males in sexual populations (half the population) are not producing offspring themselves. Because of this, an asexual population can grow twice as fast as a sexual population in theory. This means that in competition, the asexual population would have the advantage. All of these advantages to asexual reproduction, which are also disadvantages to sexual reproduction, should mean that the number of species with asexual reproduction should be more common.

However, multicellular organisms that exclusively depend on asexual reproduction are exceedingly rare. Why is sexual reproduction so common? This is one of the important questions in biology and has been the focus of much research from the latter half of the twentieth century until now. A likely explanation is that the variation that sexual reproduction creates among offspring is very important to the survival and reproduction of those offspring. The only source of variation in asexual organisms is mutation. This is the ultimate source of variation in sexual organisms. In addition, those different mutations are continually reshuffled from one generation to the next when different parents combine their unique genomes, and the genes are mixed into different combinations by the process of meiosis. Meiosis is the division of the contents of the nucleus that divides the chromosomes among gametes. Variation is introduced during meiosis, as well as when the gametes combine in fertilization.

Welcome to the Living World

(b) Suggest the ART which may be successful in the following condition:

i) Inability of the male partner to inseminate the female.

ii) Female cannot produce ovum but can provide suitable environment for fertilisation and further development. (2)

(a) Assisted Reproductive Technologies.

(b) i. Artificial insemination (AI) / Intra-Uterine insemination (IUI). Ii. Gamete Intra fallopian Transfer (GIFT).

2. Observe the diagrams A and B given below related to contraceptive methods. (3)

(b) Explain this surgical method.

(c) Why this method is generally advised as a terminal method of contraception?

(a) A. Vasectomy B. Tubectomy

(b) Vasectomy: A small part of the vas deferens is removed or tied up through a small incision on scrotum.

Tubectomy: A small part of the fallopian tube is removed or tied up through a small incision in the abdomen or through vagina.

(c) To prevent any more pregnancies.

1. Name the technique of transferring embryos up to 8 blastomeres into the fallopian tube. (1)

(a) GIFT (b) ZIFT (c) ICSI (d) IUI

2. Amniocentesis for sex determination is legally banned now. (2)

(a) Amniocentesis is a test in which amniotic fluid of the foetus is taken to analyse the foetal cells to test the presence of genetic disorders, survivability of the foetus etc.

(b) It is misused for finding out the sex of the embryo.

1. There are several methods of in vitro fertilisation to assist couples who lack the ability of fertilisation. (3)

a. Give the popular name of the programme.

b. Suggest two techniques of in vitro fertilisation and their conditions of transfer to assist these people.

(a) Test Tube Baby Programme.

(b) ZIFT (Zygote Intra Fallopian Transfer): Transfer of zygote or early embryo (with up to 8 blastomeres) into fallopian tube.

IUT (Intra Uterine Transfer): Transfer of embryo with more than 8 blastomeres into the uterus.

1. A wide range of contraceptive methods are presently available. If so,

a. Name one contraceptive method having least side effect.

b. Which contraceptive method is generally advised for females as a termination method to prevent any more pregnancies?

c. List out any two possible ill-effects of the usage of contraceptive methods. (2)

b. Tubectomy (sterilization technique)

c. Nausea, abdominal pain, breakthrough bleeding etc.

(b) Cite any two examples for STD.

(c) Suggest any two methods for the prevention of STDs. (3)

(a) Sexually Transmitted Diseases.

(b) Gonorrhoea, syphilis, genital herpes, chlamydiasis etc.

(c) Avoid sex with unknown partners/multiple partners.

Always use condoms during coitus.

1. Study the relationship between the first two words and till the blank space with a suitable word. (1)

Sterilization in male: Vasectomy

2. The incidence of STDs is reported more among the age group between 15-24 years. (2)

b. Suggest methods to prevent STDs.

(a) STDs are the diseases transmitted through the sexual intercourse.

(b) Ÿ Avoid sex with unknown partners/multiple partners.

Ÿ Always use condoms during coitus.

1. Different contraceptive methods are given below. Pick out the odd one. (1)

(c) Multiload 375 (d) Lippes loop

2. Sexually transmitted disease (STD) are mainly transmitted through sexual contact. (3)

Multiple Choice

What is a likely evolutionary advantage of sexual reproduction over asexual reproduction?

  1. sexual reproduction involves fewer steps
  2. less chance of using up the resources in a given environment
  3. sexual reproduction results in greater variation in the offspring
  4. sexual reproduction is more cost-effective

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Which type of life cycle has both a haploid and diploid multicellular stage?

  1. an asexual life cycle
  2. diploid-dominant
  3. haploid-dominant
  4. alternation of generations

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Which event leads to a diploid cell in a life cycle?

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Cabbage: Origin, Production and Breeding Methods | India

After reading this article you will learn about:- 1. Origin of Cabbage 2. Production of Cabbage 3. Cytology 4. Floral Biology 5. Qualitative Genetics 6. Cabbage as a Self-Incompatibility Vegetable7. Genetic Resources 8. Breeding Objectives 9. Breeding Methods 10. Resistance Breeding 11. Tissue Culture and Transgenic Technology 12. Selection Techniques 13. Seed Production 14. Varieties.

  1. Origin of Cabbage
  2. Production of Cabbage
  3. Cytology of Cabbage
  4. Floral Biology of Cabbage
  5. Qualitative Genetics of Cabbage
  6. Cabbage as a Self-Incompatibility Vegetable
  7. Genetic Resources of Cabbage
  8. Breeding Objectives of Cabbage
  9. Breeding Methods of Cabbage
  10. Resistance Breeding of Cabbage
  11. Tissue Culture and Transgenic Technology of Cabbage
  12. Selection Techniques of Cabbage
  13. Seed Production of Cabbage
  14. Varieties of Cabbage

1. Origin of Cabbage:

Modern hard-head cabbage cultivars originated from wild non- heading brassicas somewhere in the eastern Mediterranean and Asia Minor region.

Cabbage belongs to the cruciferae family and the species Brassica oleracea is divided into:

var. acephala – kale and collords

var. fimbriata – curly kale

var. botrytis – cauliflower

var. gemmifera – Brussels sprouts

var. italica – sprouting broccoli

All these species have the c genome, contain the same number of chromosomes (2n=2x=18) and readily cross with each other.

Brassica oleracea subsp. capitata (2n = 2x = 18) is one of the most important vegetables grown throughout the world. It has wide adaptability, high disease and stress resistance, high yield potential and strong transporting tolerance.

It is cultivated in many countries, especially those in Europe, North America and Asia. India grows cabbage in approximately 3.10 lakh hectares with an average productivity of 221 q/ha. Cabbage producing major states in India are UP, Orissa, Bihar, West Bengal, Maharashtra and Karnataka.

According to FAO-Statistics-2006, cabbage was grown in 129 countries in 2005 on an area of 3.2 million ha. As per this statistics, China occupied I rank (1.7 mha), followed by India (0.128 mha) and Russia (0.168 mha).

It must be mentioned that as per FAO-Statistics, the term cabbage includes red, white, and savoy cabbages, Chinese Cabbages, Brussels sprouts, green kale and sprouting broccoli. All these belong to Brassica oleracea with the exception of Chinese cabbage which is Brassica rapa. The countries with the highest cabbage productivity are South Africa (640 q/ha) followed by Korea (635 q/ha).

3. Cytology of Cabbage:

Cabbage has a somatic chromosome number of 18 and its genome is c. It is a secondary polyploid with basic chromosome number 6. Three basic chromosomes are present in duplicate and remainder are single i.e. ABBCCDEEF = 9.

Molecular genetic work, using restriction fragment length polymorphisms (RFLPs), suggests that this picture may be an over-simplification. In the course of constructing an RFLP map in B. oleracea, there is evidence of duplicate loci which mapped to different chromosomes.

The order of duplicate loci is often different on different chromosomes. Considerable chromosome rearrangement and restructuring has occurred during the evolution of the species. It might be difficult to identify the possible structure of a lower chromosome number progenitor or to determine if B. oleracea evolved by duplication of loci and complex rearrangements.

Fig. 19.1 shows the interrelationships of various Brassica species, genome designations and chromosome numbers.

All these six Brassica species and radish (Raphanus sativus, 2n=18) have been intercrossed with great difficulty utilizing embryo culture. Thus, the amphidiploids of Fig. 19.1 originated in nature from crosses between the parental species.

4. Floral Biology of Cabbage:

A cabbage flower has four sepals, four petals, six stamens in tetradynamous condition (two short and four long stamens) and a bicarpellary ovary which is superior and has a false septum. Ovules are attached on both the sides of septum. Two active nectaries are located between the bases of short stamens and ovary. The buds open under pressure of rapidly growing petals and become fully expanded in about 12 hrs.

Flowers are slightly protogynous and cabbage is naturally cross-pollinated due to sporophytic self-incompatibility. Pollination is brought about by bees and flies. Bud pollination is effective to achieve selfing. For cross-pollination flower buds expected to open within 1-2 days are emasculated and are pollinated immediately with desired pollen using a brush/flower stamens.

5. Qualitative Genetics of Cabbage:

All the botanical varieties within B. oleracea are cross-compatible with one another and F1 hybrids normally appear intermediate in form between the parental lines. Table 19.1 lists the inheritance of characters which are most easily identified in hybrid seedlings.

The gene list as summarised by Dickson and Wallace (1986) is given in Table 19.2.

6. Cabbage as a Self-Incompatibility Vegetable:

Cabbage is primarily self-incompatible indicated by setting of few seeds only after self- pollination. Genetically, it is sporophytic system where pollen reaction is determined by the genome of the somatic tissue (of the sporophyte) on which the pollen grain develops.

The system of self- incompatibility is characterised by the following features:

(i) Incompatibility is controlled by one S locus having multiple alleles (50-70 alleles in B. oleracea).

(ii) The reaction of pollen is determined by the genotype of the sporophyte on which pollen is produced and therefore is controlled by two S alleles.

(iii) All the pollen of a plant have similar incompatibility reaction.

(iv) The two S alleles may show co-dominance (independent action) or may interact by one being dominant over the other.

(v) The independence/dominance relationships of S alleles in pollen and in the pistil may differ.

(vi) It is usually associated with tri-nucleate pollen and inhibition of pollen occurs at the stigmatic surface.

In contrast to this in gametophytic system of self-incompatibility, the pollen reaction is determined by the genotype of the gametophyte i.e. pollen/egg cell itself and in this system the pollen is bi-nucleate and inhibition of pollen tube occurs in the style.

Various kinds of S allele interactions in a heterozygous genotype (S1S2) with sporophytic self-incompatibility could be as follows:

Mutual weakening – No action by either allele

Intermediate gradation – 0-100% activity by each allele

Table 19.3 shows the complexity of the system involving a cross S1S3 X S1S2.

Assessment of Self-Incompatibility:

The usual procedure is to count the number of seeds/pod under self-pollination (bagging of a branch of flowering stalk after removing all open flowers) vs. that under cross or open- pollination.

The disadvantage of this method is that one has to wait for about 60 days till seed reaches to maturity after pollination and secondly, the number of seeds reaching to maturity may also be reduced, by disease, water stress, high temperature in tropics and other stresses.

Ability of fluorescent microscope to display readily those pollen tubes that have penetrated the style provides a direct measure of incompatibility that can be assessed within 12-15 hr. It is adequate and more convenient to be used in a large breeding programme. Pollinated flowers 16-30 hr after pollinations are collected and excised ovaries are softened in 60% NaOH, and placed in aniline blue for staining.

At about 48 hr, after pollination, stigma and style are squashed on a microscope slide. The aniline blue stain accumulates in the pollen tubes and fluoresces when irradiated with UV light thus, under a fluorescent microscope the tubes are visible, whereas the background of stylar tissues is largely unseen.

Penetration of style by none or few tubes indicates incompatibility, penetration by many tubes indicates compatibility and penetration by intermediate number indicates intermediate level of incompatibility.

Permanent S Allele Identities:

The National Vegetable Research Station (NVRS) at Wellesbourne, Warwick, UK has a collection of all known S alleles. The individual breeder may develop homozygous inbreds through selfing in bud stage and tentatively allot the genotypes as SaSa or SbSb.

If SaSa is demonstrated to be reciprocally incompatible with s3s3 maintained at NVRS, SaSa shall be of S3S3 genotype under international nomenclature. However, breeders can also assign S alleles on their own and maintain the inbreds under the designated S allele nomenclature.

Breakdown of Self-Incompatibility:

Various techniques as listed below are available for obtaining a temporary breakdown of the self-incompatibility.

(ii) Delayed self-pollination

(v) Application of carbon dioxide

(vi) Hormones and protein inhibitors

(viii) Acute irradiation of styles

(ix) Acute irradiation of pollen mother cells

(xii) Treatment of stigma with organic solvent

(xiii) End-season pollination

(xiv) Steel brush pollination

(xvi) Electric aided pollination

Biochemical Basis of Self-Incompatibility in Brassica:

Nishio and Hinata (1977) carried out polyacrylamide gel isoelectric focusing to study buffer soluble proteins of stigmatic homogenates of six S-allele genotypes in Brassica oleracea.

Six strains with S-alleles as S2S2, S7S7, S13S13, S22S22, S39S39 and S45S45 were provided by Institute for Horticultural Plant Breeding, the Netherlands. From open flowers, 50 stigmas were homogenized by a mortar and pestle with 0.1 ml phosphate buffered saline (0.01 M phosphate buffer pH 7.1 plus 8.5 g/1 of NaCl).

The homogenate was centrifuged for 20 minutes at 10,000 rpm and 20 of the supernatant was introduced to each glass tube. Proteins were extracted from anthers, leaves and seedlings. Polyacrylamide gel electrophoresis and isoelectric focusing were used. However, results from isoelectric focusing were found to show S-allele specificity ascribable to a combination of the protein bands.

In this method 7.5% acrylamide gel containing ampholine (pH 3.5-10.0) was used. Sample gel was faced to the anode side. Anode and cathode vessels were filled with 0.02 M HCl and 0.02 M ethylene diamine, respectively. Electrophoresis was carried out under constant voltage, 200 V, for 3 hours at 5°C.

The gels after running were immersed in 12.5% trichloroacetic acid overnight, and washed in 7% acetic acid 4-5 times to remove ampholine. The gels were stained with 0.2% Coomassie Blue in ethanol-water-acetic acid (45 : 45 : 10) for 45 minutes and then de-stained with ethanol water acetic acid (25 : 65 : 10) and then stored in 7% acetic acid.

It is known in Brassica that S-allele specificity appears in mature stigmas but not in young ones. Therefore, the basic proteins of the stigmas were compared between young and old. The densitometry of the band pattern of young and mature stigmas in S13S13 homozygotes is shown in Fig. 19.2.

The diagrammatic representation of stigmatic proteins of different S-homozygotes as observed under isoelectric focusing by Nishio and Hinata (1977) is shown in Fig. 19.3. Perusal of Fig. 19.3 indicates that S39S39 hand d, e, f, g and i bands, while S13S13 had e, g, h, i, and trace of d, etc. The band e was observed in every homozygote.

All the S-homozygotes were differentiated by the combination of these bands. There is a possibility that these bands are not S-allele specific but are products of the genetic backgrounds of the S-homozygotes. Similar patterns of zymograms were, however, found in stigmas of different S-homozygotes for esterase, acid phosphatase, and peroxidases.

Further, no discernible specificity was found in leaf and seedling proteins of different S-homozygotes by the isoelectric focusing. It may be inferred, therefore, that background of the material was not so different between S-alleles.

The protein bands focused in the present method appeared in the course of the maturation of stigmas and the time of appearance coincided with the phenotypic expression of self-incompatibility. The balance of evidence suggests, therefore, that some, it not all, of the fractions revealed by the isoelectric focusing are directly related with the specificity of S-alleles.

These stigmas extracts have now been specifically recognized as S-locus specific glycoproteins (SLSG) and exhibit extensive polymorphisms that are most easily detected on is electric focusing gels.

Following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of stigma extracts, SLSGs migrate as a complex of several closely spaced molecular-weight species differing by approximately 2000 Daltons.

7. Genetic Resources of Cabbage:

Plant genetic resources are the backbone of any crop breeding programme. Since 1982, the IPGRI has sponsored several missions to collect wild Brassica species.

According to IPGRI policy, each sample is split into 3 parts which are stored at:

1. Poly-tech University, Madrid, Spain

2. University of Tohoku, Sendai, Japan

3. Gene Bank of country from where samples are collected

In USA, the National Plant Germplasm System (NPGS) is a cooperative effort by public (State and Federal) and private organisations to conserve plant genetic resources. As of 16 July 2006, the NPGS holds a total of 471318 accessions that represent 216 families, 1914 genera and 11756 species. Most Brassica species are conserved at Plant Genetic Resources Unit (PGRU) at Geneva Campus, (New York) of Cornell University.

In 1982, Prof. Williams established the Crucifers Genetics Cooperative (CrGC) at the Univ. of Wisconsin to manage germplasm of Brassicaceae. European brassica database (Bras -EDB) has been developed by the centre for Genetic Resources, the Netherlands. Other European countries that maintain collections of cabbages and kales are Bulgaria, Croatia, Czech Republic, Hungary, Poland, Russia, Switzerland, and Turkey.

According to Swarup and Brahmi (2005), there are sizeable collections of cole crops in Israel. Ethiopia, South Africa, India. Philippines and Taiwan. The IARl-Regional Station. Katrain, Kullu Valley, Himachal Pradesh is actively engaged in cabbage germplasm maintenance and breeding research in India.

8. Breeding Objectives of Cabbage:

2. Longer staying capacity in field after head formation/greater field holding capacity

3. Desirable heal weight (1 – 1.5 kg)

4. Early head formation/early maturity

6. Head shape and colour as per preference of consumers (essentially round heads, light green-green colour)

7. Less proportion of outer/wrapper leaves

9. Firm head with short internal stem

10. Ability to tolerate frost

11. Resistance to diseases:

i. Black rot (Xanthomonas campestris)

ii. Alternaria leaf spot (Altemaria ssp.)

iii. Black leg (Leptosphaeria maculans)

12. Tolerance to insect – Pests

– Diamond – back moth (Plutella xylostella)

9. Breeding Methods of Cabbage:

Open-pollinated Cultivars:

(ii) Inbreeding (in cultivars with low level of self-incompatibility and inbreeding depression)

The self-incompatibility is used to produce hybrid seeds in cabbage and other cole crops, namely, cauliflower, broccoli, Brussels sprouts, and kale. The individual plants are self-pollinated through bud-pollination. Selection is applied for desirable characters and strong level of self-incompatibility.

This way several self-incompatible, but cross-compatible inbreds having different S-alleles are developed as illustrated in (Fig. 19.4).

Such S1S1 and S2S2 lines are planted in alternate rows in isolation and seed set on each line will be mostly hybrid seed where cross-fertilization is brought about by pollinating insects, mostly bees. The cross compatibility between inbreds of S1S1 and S2S2 assures the production of F1 hybrid seed.

Cabbage hybrids could be of following kinds:

This is a cross between two inbreds. Single cross hybrids are more uniform than hybrids produced from double/top crosses.

A cross between two single crosses is known as double cross. Four homozygous inbreds are required to produce a double cross, for example, (S1S1 x S2S2) X (S3S3 x S4S4). In this system, seed is harvested from both the single crosses which themselves are vigorous and therefore, cost of hybrid seed is reduced.

This is a cross between a single self-incompatible inbred line as female and a good open- pollinated cultivar as pollen parent. Till, late eighties, most of the cabbage hybrids produced in United States were top crosses.

Problems in the Breeding of F1 Hybrids:

(i) Depression by inbreeding

(ii) Sister-brother fertilization within parental lines creating the problem of ‘sib’ seed contaminants

(iii) Reduction of incompatibility by environmental conditions

(iv) Restriction of pollination within parental lines by bees instead of random movement of bees

Depending upon the parental lines and conditions during seed production, the proportion of such sib seed may vary from nil to as much as 80%. The usual method of assessment of proportion of sibs is to grow plants from a seed sample until they are sufficiently developed to adjudge phenotypic difference between sibs and hybrids.

The time taken may vary from a few weeks if obvious differences are apparent at the seedling stage, to from 10-12 weeks if difference between the hybrid and parents cannot by adjudged until the adult plant stage. In such situations, isozyme analysis as standardised by Wills (1979) has been shown to have several advantages and offers a practical alternative to traditional methods.

In this method extracts of seed of Brassica oleracea L. cultivar were separated by electrophoresis on polyacrylamide gels and stained for 14 enzymes, namely:

xii. Leucine amino peptidase

The electrophoresis was carried out on 10% polyacrylamide gel slabs with gel buffer 0.37 M tris-HCl, pH 9.1 and electrode buffer 0.01 M tris-glycine, pH 8.3. Acid phosphatase activity was found in 3 anodal zones. The fastest zone stained too faintly to permit consistent analysis. The densely staining slowest zone could not be resolved into discrete bands.

The intermediate zone was highly active and except for one cultivar, all seeds showed either one or two of the total five bands recognized. Hybrid seeds from crosses between inbreds with different single bands expressed both parent bands as illustrated in Fig. 19.5. Fitzgerald (1997) have described a technique for determining sib-proportion and aberrant characterisation in hybrid seed using image analysis.

Breeding and Utilisation of Self-Incompatible Lines:

It is easy to breed self-incompatible lines of cabbage through continuous self-pollination and selection. When two self-incompatible lines are used as parents to produce hybrids, the reciprocal crossed seeds can be harvested as hybrids. In 1950, the first cabbage hybrid in the world was developed in Japan using self-incompatible lines. This hybrid was known as Nagaoka No. 1.

The superior self-incompatible lines for hybrid seed production should have following characters:

1. Stable self-incompatibility

2. High seed set after self-pollination at bud stage

3. Favourable economic characteristics

4. Desirable combining ability

5. Almost all cabbage hybrid seeds are produced using self-incompatible lines all over the world. Now CMS system is also being used.

Bud Pollination:

The basic seed of parental inbred lines is obtained by hand selfing at bud stage. The bud top is removed by tweezers and strippers to expose stigma which is then pollinated with pollen collected from the same plant/line. The seed production plot of parental inbred lines is covered with net to avoid contamination by bees or other insects.

Pollen grains are collected afresh from the opened flowers on the same day. The mixed pollen collected from the same line should be used for pollination to avoid viability depression from continuous selfing.

If the bagging isolation is applied to multiply the basic seeds, the flowering branch is covered with paraffin bag/muslin cloth bag before the bud opens. The bud size should not be too small or big. Bud pollination done 2-4 days prior flowering gives the highest seed set.

Propagation of basic seeds of incompatible lines by bud pollination is labour-intensive and costly. In consideration of this disadvantage, the electricity-aided pollination, wire brush pollination, thermal-aided pollination, CO2 enrichment, etc., have been suggested.

However, each one of these has its limitations and has not been used on commercial scale. Spraying a solution of 5% common salt has been used to overcome the self-incompatibility and increase the seed set by scientists in China. This method has been successful in the propagation of basic seeds.

Special Considerations for F1 Hybrid Production Plots:

1. Isolation distance of at least 2000 m from cauliflower, kohlrabi, broccoli, kale, Brussels sprouts, etc.

2. Provision of approximately 15 honey bee boxes/ha

3. Building-up framework through appropriate staking to prevent lodging

4. Control of insects and diseases

5. Synchronized flowering of the parental inbreds

6. Planting ratio of 1: 1 for the parental inbreds

7. Although harvested seeds from both parents can be mixed-up, it is better to harvest seeds from both the inbreds separately to improve seed uniformity.

10. Resistance Breeding of Cabbage:

Cabbage Yellows:

It is caused by Fusarium oxysporum. It is soil borne, vascular wilt favoured by warm soil temperatures with optimum at 28°C. There is progressive yellowing followed by brown necrosis, stunted plant growth with premature leaf drop. Type A resistance is determined by one dominant gene and is not influenced by temperature.

Type B resistance is conditioned by several genes and breaks down at temperature above 22°C. Screening for A type resistance is done by dipping young seedlings in an inoculation suspension and then growing them at 27°C. In 2-3 weeks susceptible plants will be dead.

It is a bacterial disease caused by Xanthomonas campestris. Resistance was reported in Early Fuji. It is seed borne, shows vascular bacteriosis causing yellowing of leaves. Resistance is controlled by a major gene ‘f’ plus 2 modifiers, one dominant and one recessive.

For artificial inoculation a bacterial suspension is sprayed on well-developed plants early in morning. This introduces bacteria into guttation droplets. In 2-3 weeks, susceptible plants will develop large lesions on leaf margins and blackening through veins of leaf and stem. Resistant cultivars will show slight necrotic infection at leaf margins.

11. Tissue Culture and Transgenic Technology of Cabbage:

Anther culture and microspore culture have been reliably used to produce double haploid lines. The double haploids allow rapid establishment of homozygous lines from wide crosses. Successful anther and microspore cultures have been reported for several crops in B. oleracea including cabbage. Double haploids have been of importance in mapping of genes and to detect QTLs.

Transgenic cabbage and kale cultivars with enhanced resistance have been produced, while transgenic canola (B. napus) has been commercialized in USA, there are no GM vegetable brassica. The most general approach for genetic transformation in cabbage has been through Agrobacterium tumefusiens and A. rhizogenes.

The explant for transformation in cabbage is leaf petiole, hypocotyl and leaves. Mostly, transgenic cabbages have foreign gene from Bacillus thuringiensis (Bt gene). Bt genes have been expressed in all the major groups of brassica crops including kales and cabbages.

Private sector seed companies have produced cabbage Bt transgenics and field level evaluations have also been done. However, no Bt brassicas have been released commercially.

Transgenic cabbage resistant to P. xylostella (diamond back moth) has been developed through A. tumefaciens – mediated transformation with B. thuringiensis (Bt) cry genes. The genes used to produce transgenic cabbage against DBM are Cry I Ac, cry 1 Ab3 and cry 1 Ab including cry 1 Ab transgenic in India by Bhattacharya (2002). Resistance induced has been partial with delayed insect development rather than insect mortality.

Protocols for tissue culture and Agrobacterium tumefaciens-mediated transformation of cabbage have been developed. Factors important for transformation include pre-culture and co-culture of explants on a callus induction medium, induction of Agrobacterium virulence with a minimal medium containing acetosyringone, use of an appropriate amount and initial application of selective agents.

A synthetic Bt toxin gene, cry1 Ab3, and a wild-type gene, crylla3, have been used for transformation. All cabbage plants transgenic for cry1 Ab3 provided 100% mortality of the larvae of the diamondback moth, whereas cabbage plants transformed with crylla3 were susceptible to the larvae.

Northern analysis showed that the transgenic cry1 Ab3 plants produced a full-length transcript of gene, whereas the cry1 1/a3 plants produced a truncated transcript, leading to the susceptibility of these plants to the diamondback moth.

Thus, cabbage has been transformed to express Bt ICPs for control of the diamondback moth but here transgenic cabbage has been used primarily to evaluate management strategies, although seed companies are evaluating the potential for commercialisation.

Great care must be taken to develop such plants because DBMs have already developed high levels of resistance in some areas to foliar applications of Bt products containing cry1 A and cry1 C toxins.

12. Selection Techniques of Cabbage:

Pointed, flat, or round heads are preferred depending upon consumers’ appeal. Generally, round heads with internal solidity are selected. Shape of head is usually expressed in terms of polar and equatorial diameters of head and their ratio as given below:

Spherical head – ratio is 0.8 -1

Drum head – ratio is 0.6 or less

Conical head – ratio is more than 1

Heading Vs Non-heading:

The wrapper leaves surrounding the terminal buds should be tight enough to form a head.

Medium sized heads are generally desirable.

A short stem is desirable because tall stemmed plant will not be able to bear the weight of the cabbage head and consequently, tall plant is likely to fall.

A narrow core is desirable.

A short core less than 25% of the head diameter is preferred.

A soft core is preferred over tough one, particularly in cabbage meant for processing.

This is undesirable and is assessed by splitting the head vertically through the core.

Longer storability is desirable. It is positively correlated with dry matter contents and late maturity. Dry matter could be assessed by sampling about 200 g portion of head excluding core tissue and measuring the fresh and dry weights of the sample.

Head Compactness:

By applying pressure on head by thumbs, compactness of the head can be judged to some extent. Following 4 methods are more useful.

(i) Examination of the position of the uppermost wrapper leaf indicates compactness. If it covers two third or more area of head, the head is considered to be compact.

(ii) Measuring the length of core inside the head by cutting a longitudinal section also indicates compactness. A compact head has relatively small core.

(iii) Compactness of the head can also be adjudged by the following formula given by Pearson.

Where Z = an index of compactness

C = net weight of the head

W = average of the lateral and polar diameters of the head. A higher value of Z indicates more compact head.

(iv) Net weight of head (without stalk and non-wrapper leaves) also gives a fair idea of compactness. More the weight, higher is the compactness.

Frame of the Plant:

This is the maximum spread of plant at maturity. Usually smaller frames are preferred.

13. Seed Production of Cabbage:

Isolation Distance:

1. Breeder/Foundation seed – 1600 m

Cultivar Description of Cabbage:

There are open-pollinated and F1 hybrid cultivars. The following outlines for cultivar descriptions of cabbage are based on the guidelines for DUS tests produced by UPOV (1992) and described by George (1999).

1. Plant height: very short, short, medium, tall or very fall

Maximum diameter: small, medium or large

Length of outer stem: short, medium or long

Attitude of outer leaves: erect, semi-erect or horizontal

3. Outer leaf: Small, medium or large

Shape of blade: broad elliptic, broad ovate, circular, transverse broad elliptic or broad obviate

Profile of upper side of blade: concave, plane or convex

Blistering: absent or very weak, weak, medium, strong or very strong

Size of blisters: small, medium or large

Crimping (savoy cabbage only): weak, medium or strong

Colour (with wax): yellow-green, green, grey-green, blue-green or violet

Intensity of colour: light, medium or dark

Green flush (red cabbage only): absent or present

Waxiness: absent or very weak, weak, medium, strong or very strong

Undulation of margin: absent or very weak, weak, medium, strong or very strong

Incisions of margin: absent or present

Reflex-ion of margin: absent or present

Shape of longitudinal section: transverse narrow elliptic, transverse elliptic, circular, broad elliptic, broad obovate, broad ovate or angular ovate

Shape of base in longitudinal section: raised, level or arched

Length: short, medium or long

Diameter: small, medium or large

Position of maximum diameter: towards top, at middle or towards the base

Cover: uncovered, partially covered or covered

Blistering of cover leaf (savoy cabbage only): absent or very weak, weak, medium, strong or very strong

Reflex-ion of margin of cover leaf: absent or present

Colour of cover leaf: yellow-green, green, grey-green, blue-green or violet

Intensity of colour of cover leaf: light, medium or dark

Anthocyanin coloration of cover leaf (white and savoy cabbages only): absent or very weak, weak, medium, strong or very strong

Internal colour: whitish, yellowish, greenish or violet

Intensity of internal colour (red cabbage only): light, medium or dark

Density: very loose, loose, medium, dense or very dense

Internal structure: fine, medium or coarse

Length of interior stem (in relation to length of head): short, medium or long

5. Time of harvest maturity (in specific season): very early, early, medium, late or very late

6. Time of bursting of head after maturity: early, medium or late

7. Resistance to race 1 of Fusarium oxysporum f. sp. conglutinans

8. Method of seed production: open-pollinated or hybrid

3. Seed multiplication ratio – 100

14. Important Varieties of Cabbage:

Based on maturity, head shape, head size, and leaf colour and shape cabbage varieties have been classified into different groups:

(i) Wakefield or Winningstadt group

(ii) Flat Dutch or drumhead group

(iii) Copenhagen market group

In India Copenhagen market group (early round headed varieties with compact heads having few outer leaves and small core) and Flat Dutch group (flat heads, large outer leaves) are common.

Copenhagen Market:

It has round heads which are bigger than that of Golden Acre. Head weight is 1.5-3.0 kg. It takes 75-85 days for head formation.

An earliest variety, selection from Copenhagen market, 60-65 days from transplanting to head formation, 1-1.5 kg head, solid head with short core, prone to cracking under delayed harvesting, recommended by Indian Agricultural Research Institute, New Delhi.

An introduction recommended by Dr. Y.S. Parmar University of Horticulture and Forestry, Solan, bigger head (1.5-2.0 kg). Basically, it is also a selection from Copenhagen Market.

Pusa Mukta (Sel-8):

Developed from an inter-varietal cross of EC 24855 and EC 10109 at IARI, regional Station, Katrain, Kullu Valley, Himachal Pradesh, early with medium sized round heads, slightly late than Golden Acre, resistant to black rot, identified by all India coordinated vegetable improvement project and released by central sub-committee on Crop Standards, Notification and Release of Varieties.

It is the first tropical variety developed for cultivation under high temperature conditions. It can grow and form heads at a temperature of 15-30°C. It takes 70-90 days for head formation after transplanting. It has grey-green foliage and flattish-round heads. Head weight is 600-1200 g. Its seeds can be produced under sub-tropical conditions of north-Indian plains.

Developed by selection at Katrain, early in Drum Head group, big sized flat heads (3-4 kg) in 70-75 days after transplanting, resistant to black leg (Phoma lingam).

An introduction from the then German Democratic Republic under INDO-GDR Project in Nilgiri Hills. The initial seeds were received through NSC and showed wide variation. The same has been purified at Katrain. Heads are solid, flattish round to slightly oblong weighing 3-5 kg. The foliage is dark green with wavy margin. It is popular in Nilgiri hills of Tamil Nadu and has been recommended by Tamil Nadu State Department of Horticulture.

Savoy cabbage having blistered leaves is not popular in India. The heads are pointed, round and flat. Commonly catalogued variety is Chieftain. Red cabbage group (variety-Red Acre) is also not popular in India. Some promising hybrids are Bajrang, Swarna, Sudha, Sri Ganesh Gol, Bahar, Pragati, Hari Rani Gol, Kranti, etc. in India.

Roughly 100 ton OP cabbage seed and 50 ton hybrid cabbage seed is marketed in India. All hybrid cabbages are imported. Some of the cabbage hybrids imported from abroad (China, Japan, Korea, Taiwan) are tropical types and hence, cabbage is available in Indian market round the year.

Adaptations to increase reproductive success

It is important to keep in mind that adaptations (anything that increases an individual’s reproductive success) occur without conscious thought or intention on the part of the individual see the Bio1510 website pages on “What is Evolution?” and “Evolution by Natural Selection” for help with this often confusing concept. The result of these types of selection is the evolution of different strategies for maximizing biological fitness, or reproductive success relative to others in the population. An individual who has, for example, 10 surviving offspring (who then go on to reproduce as well) has higher fitness than an individual who has 7 offspring surviving offspring.

There are many different types of adaptations in different species to maximize biological fitness, including parental investment, direct male competition, and indirect male competition. These concepts are described below:

Parental investment is any energy, effort, or resource that a parent provides to increase the offspring’s chances of survival, but at the cost of the parent’s ability to invest in other offspring. Parental investment can include all types of parental care, as well as energy resources deposited in the egg or other nutrition provided to the developing embryo. It occurs both in species that reproduce via internal fertilization as well as those that reproduce via external fertilization. Some examples are shown below:

The male of the common midwife toad, Alytes obstetricans, carries the fertilized eggs on his hind legs until they are ready to hatch. By Christian Fischer, CC BY-SA 3.0,

Like many bird species, hummingbirds provide food to their hatchling until the young birds are ready to leave the nest. By Wolfgang Wander, Papa Lima Whiskey (edit) – self-made /, CC BY-SA 3.0,

Males often engage in direct male competition over potential mating partners. This type of competition occurs when females mate only with a single male, typically the “winner” of the competition. Direct male competition often includes aggression (fighting) between males, but there are other forms as well.

Examples of direct male competition include:

  • Male-male aggression: males fight with each other for access to females
  • Courtship rituals: males engage in “dances” or other displays to attract females
  • Lekking: a specialized form of courtship ritual where many males gather together in one place and “display” at the same time, allowing females to choose among them

Male-male aggression in Mallard ducks. Image credit:
Ken Clifton/Flickr

It’s not all just competition between males females choose which males to mate with based on observing the male competition. Selection of the “best” male by females is called female choice or intersexual selection. Female choice (intersexual selection) and direct male competition (intrasexual selection) usually lead to selection for extremely “showy” traits that don’t appear to provide any benefit to the individual’s survival, and might even make it more likely for the animal to be eaten by a predator (think of the peacock’s tail – see below). But if the trait improves the male’s ability to produce successful offspring because more females choose to mate with him, then these traits do in fact improve an individual’s biological fitness, even at the cost of decreasing its survival!

One question is why females should “care” about these showy male traits. A leading hypothesis to answer this question is the good genes hypothesis, which is the idea that these sexually-selected, showy male traits are “honest indicators” of good genetic quality. In other words, it takes good genes to make a big flashy tail (and to avoid being eaten by a predator, since that big tail slows him down), so the bigger and showier the tail, the “better” the male.

The peacock’s tail is used on courtship displays to attract females. Females prefer males with larger, more colorful tails. Image credit:
Özgür Mülazımoğlu/Flickr

This video gives a brief overview of the implications of the good genes hypothesis and sexual selection in humans:

Instead of (or in addition to) competing directly with each other to have the opportunity to mate with a female, males can also compete for fertilization of a female’s eggs after mating has already occurred! Competing after mating is also called indirect male competition, or sperm competition, and it results in one male being more successful than another at fertilizing a female’s eggs. This type of competition occurs in species where the female is likely to mate with multiple males, so instead of males directly competing with each other, they are competing via their sperm. In other words, if a female mates with more than one male, then any male whose sperm end up fertilizing more eggs is going to have more offspring, on average, than other males.. So if there is a trait that makes this male’s sperm more successful than other male’s sperm, then that trait is going to end up increasing in the population over generations.

Examples of traits which typically confer first male advantage include:

  • Mate guarding: a male remains close by the female after mating, preventing other males from mating with her until there has been time for his sperm to fertilize the eggs
  • Copulatory plugs: the male’s ejaculate includes a sticky residue which temporarily blocks entry to the female’s reproductive tract, making it difficult for other males to mate with her until after there has been time for the first male’s sperm to fertilize the eggs

Examples of traits which typically confer second male advantage include:

  • Elaborate penis morphology: elaborate structures on the penis help remove the sperm of previous males from the female’s reproductive tract by essentially scraping out the previous ejaculate
  • Large ejaculate volume and large testes: a large volume of ejaculate helps to flush out the sperm deposited in the female’s reproductive tract by the previous male a large ejaculate volume means the testes must also be large, in order to have enough space to hold all the sperm

The genitalia of the male Callosobruchus analis beetle is covered in spines from base to tip the spines facilitate removal of sperm deposited in the female’s reproductive tract by previous males. Referenced in Rönn, J., Katvala, M. & Arnqvist, G. 2007. Coevolution between harmful male genitalia and female resistance in seed beetles. Proceedings of the National Academy of Sciences 104, 10921-1092. and Hotzy, C. & Arnqvist, G. 2009. Sperm competition favors harmful males in seed beetles. Current Biology 19, 404-407.

Female anatomy can also influence the success of sperm from specific males in a process called cryptic female choice, where a female is capable of preferentially using sperm from a specific male even if she has mated with multiple males. This process is poorly understood but suggests that males competition alone does not dictate success of that male sperm in fertilizing an egg.

This video provides a great overview of sperm competition, but be aware that it erroneously refers to bonobos as having a polygymous mating system (they are promiscuous) and gorillas as being monogamous (they are polygynous):

Welcome to the Living World

India initiated reproductive health programmes (family planning) in 1951.

Now wider reproduction-related areas are in operation under Reproductive & Child Health Care (RCH) programmes.

  • Give awareness about reproduction related aspects for creating a reproductively healthy society.
  • Educate people about birth control, care of pregnant mothers, post-natal care of mother and child, importance of breast feeding, equal opportunities for male & female child etc.
  • Awareness of problems due to population explosion, social evils like sex-abuse and sex-related crimes, etc.
  • To provide right information about sex-related aspects. It helps to avoid sex-related myths and misconceptions.
  • To give proper information about reproductive organs, adolescence and related changes, safe and hygienic sexual practices, sexually transmitted diseases (STD), AIDS etc.


In 1900, world population was about 2 billion. By 2000, it rocketed to about 6 billion and 7.2 billion in 2011.

In India, population was nearly 350 million at the time of independence. It reached 1 billion by 2000 and crossed 1.2 billion in May 2011. It means every sixth person in the world is an Indian.

According to the 2011 census report, our population growth rate was less than 2% (i.e. 20/1000/year), a rate at which our population could increase rapidly.

  • Increased health facilities and better living conditions.
  • Rapid decline in death rate, maternal mortality rate (MMR) and infant mortality rate (IMR).
  • Increase in number of people in reproducible age.
  • Motivate smaller families by using contraceptive methods.
  • Aware peoples about a slogan Hum Do Hamare Do(we two, our two). Many couples have adopted a ‘one child norm’.
  • Statutory rising of marriageable age of females (18 years) and males (21 years).
  • User-friendly, easily available, effective and reversible.
  • No or least side-effects.
  • It should not interfere with sexual drive, desire & sexual act.


  • Periodic abstinence: Avoid coitus from day 10 to 17(fertile period) of the menstrual cycle to prevent conception. Fertile period is the period having chances of fertilization.
  • Coitus interruptus (withdrawal): Withdraw penis from the vagina just before ejaculation to avoid insemination.
  • Lactational amenorrhea: It is the absence of menstrual cycle & ovulation due to intense lactation after parturition. Fully breastfeeding increases lactation. This method helps to prevent conception. This is effective up to 6 months following parturition.

They prevent physical meeting of sperm & ovum. E.g.

Made of rubber/latex sheath.

Condoms for male: Cover the penis.

Condoms for female: Cover the vagina & cervix.

Condoms are used just before coitus. They prevent the entry of semen into female reproductive tract.

  • It protects the user from STDs and AIDS.
  • Easily available and disposable.
  • It can be self-inserted and thereby give privacy to user.

Made of rubber and are inserted into the female reproductive tract to cover the cervix during coitus.

They block the entry of sperms through the cervix.

Spermicidal creams, jellies & foams are used along with these barriers to increase contraceptive efficiency.

These are inserted by doctors or nurses in the uterus through vagina. They increase phagocytosis of sperms.

IUDs are ideal method to delay pregnancy or space children.

  • Non-medicated IUDs: They retard sperm motility. Also have spermicidal effect. E.g. Lippes loop.
  • Copper releasing IUDs: Cu ions suppress motility and fertilising capacity of sperms. E.g. CuT, Cu7, Multiload 375.
  • Hormone releasing IUDs: They make the uterus unsuitable for implantation and the cervix hostile to the sperms. E.g. Progestasert, LNG-20.

Oral administration of progestogens or progestogen–oestrogen combinations in the form of tablets (pills).

Pills are taken daily for 21 days starting within the first five days of menstrual cycle. After a gap of 7 days (menstruation period), it should be repeated in the same pattern till the female desires to prevent conception.

They inhibit ovulation and implantation and thicken cervical mucus to prevent entry of sperms.

Pills are very effective with lesser side effects.

Saheli: New oral contraceptive for the females. It is developed by Central Drug Research Institute (CDRI) in Lucknow. It contains a non-steroidal preparation. It is a ‘once a week’ pill with very few side effects and high contraceptive value.

Progestogens or Progestogens-oestrogen combination are used by females as injections or implants under skin.

Their mode of action is like that of pills and their effective periods are much longer.

Progestogens or progestogen-oestrogen combinations & IUDs are used as emergency contraceptives within 72 hours of coitus. It avoids pregnancy due to rape or casual intercourse.

It helps to block gamete transport and thereby prevents conception. It is very effective but reversibility is very poor.

Vasectomy: Sterilization procedure in males. In this, a small part of the vas deferens is removed or tied up through a small incision on the scrotum.

Tubectomy: Sterilization procedure in females. In this, a small part of the fallopian tube is removed or tied up through a small incision in the abdomen or through vagina.

Side effects of anti-natural contraceptives:

Nausea, abdominal pain, breakthrough bleeding, irregular menstrual bleeding, breast cancer etc.


Euglena employ a simple and primal method of reproduction, known as Binary Fission. Reproduction by binary fission involves an organism merely splitting (= fission) into two (= binary) identical halves. Since another individual of the species is not involved, binary fission is an asexual form of reproduction. The following stages can be observed during binary fission.

The most important part of binary fission is the division of the nucleus (genetic material), which occurs through a process called mitosis. Mitosis consists of four stages. During the interphase, which takes up more than 90% of the cell’s life cycle, the cell grows and stores nutrients, preparing itself for the eventual division. Interphase is not technically a part of mitosis, but is the time spent preparing for mitosis.

Then come the actual four stages of mitosis, prophase, metaphase, anaphase, and telophase.

Via these stages, the nucleus is duplicated, and both nuclei are temporarily housed in the same cell.

Through cytokinesis, the rest of the cell is duplicated and separated, resulting in two identical (albeit a bit smaller than the mother cell) daughter euglinoids, containing the two nuclei and roughly the same percentage of other organelles (‘organs’ of a cell).

As the daughter cells grow, the optimum number of various organelles is achieved. Eventually the daughter cells go through the same process themselves, preparing for the division for 90% of their lives, and after the interphase, undergoing binary fission to produce their own daughter euglinoids.

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