It is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself.


Asexual reproduction:

·         Offsprings produced by single parents.

·         Without involvement of gamete formation

·         Offsprings are genetically identical to their parents.

Methods of asexual reproduction:

·         Cell division as a method of asexual reproduction as in Protista and monera.

·         Binary fission e.g. Amoeba, Paramecium.

·         Budding: e.g. yeast.

·         Asexual reproductive structures:

o    Zoospores: aquatic fungi, Chlamydomonas.

o    ConidiaPenicillium.

o    Bud: Hydra

o    Gemmulessponges.

·         Vegetative propagation units in plant: (Vegetative propagules)

o    Runner, rhizome, sucker, tuber, offset, bulb.

Sexual reproduction:

·         Involvement of single or two individual.

·         Production of male and female gametes ( haploid)

·         Gametes fused to form a diploid zygote.

·         Zygotes developed into new organism.

·         The offsprings are not genetically identical with their parents.

Features of sexual reproduction:

·         Period between birth and sexual maturity is called juvenile phase. It is known as vegetative phase in plant.

·         Bamboo species flower only once in their life time generally after 50-100 yr.

·         Strobilanthus kunthiana (neelakranji) flowers once in 12 years.

·         Oestrus cycle: cyclical changes during reproduction in non-primate mammal like cows, sheep, rats, deers, dogs, tiger etc.

·         Menstrual cycle: cyclical changes during reproduction in primate mammals like monkeys, ape, and humans.

·         Seasonal breeders: reproductive cycle takes place in favourable seasons as in wild animals.

·         Continuous breeders: reproductively active throughout their reproductive phase.

Pre-fertilization events:

·         Process of gamete formation is gametogenesis.

·         Two gametes are similar in appearance are called homogametes (isogametes).

·         Gametes produced are of two morphologically distinct types called heterogametes.

·         Male gamete is called antherozoids or sperm and the female gamete is called ovum or egg.

Sexuality in organism:

·         Plant having both male and female sex organ called homothallic or monoecious.

·         Plants having only one sex organ is called heterothallic or dioecious.

·         In flowering plants, the unisexual male flower is staminate, i.e. bearing staments, while the female is pistillate or bearing pistils.

·         Animal having one type of reproductive system, called unisexual.

·         Animal having both male and female reproductive system, called hermaphrodite or bisexual.

Cell division during gamete formation:

·         Gametes in all heterogametic species two types namely male and female.

·         Gametes are always haploid irrespective of parent’s ploidy.

·         A haploid parent produces gametes by mitotic division.

·         Diploid parent produces gametes by meiotic division.

·         In diploid organisms specialized cells called meiocytes (gamete mother cell) undergo meiosis to produce haploid gametes.

Gamete transfer:

·         Male and female gamete must be physically brought together to facilitate fusion called fertilization.

·         In most cases male gametes are motile, female gametes are non-motile.

·         In case of few fungi and algae, both male and female gametes are motile.

·         In most cases water is the medium for gamete transfer.

·         Male gametes are produced in several thousand times the number of female gametes produced to compensate the loss during transfer.


·         Fusion of male and female gamete is called fertilization or syngamy.

·         The female gamete undergoes development to form new organism without fertilization. This phenomenon is called parthenogenesis.

·         Gametic fusion takes place outside the body i.e. water is called external fertilization.

·         Their must be synchrony of gamete release, large number of gametes released to enhance the chance of fertilization.

·         Enable the individual to produce large number of offsprings.

·         A major disadvantage is that the offsprings are extremely vulnerable to predators.

·         Fertilization takes place inside the body is called internal fertilization.


·         Formation of zygote after fertilization is universal in all sexually reproducing organisms.

·         Zygote is formed usually in water in case of external fertilization.

·         Zygote is formed inside the body of the organism in internal fertilization.

·         Zygote of fungi and algae develops a thick wall that is resistant to dessication and damage.

·         Organism with haplontic life cycle, zygote undergoes meiosis to produce haploid spores.



·         Development of zygote into an embryo is called embryogenesis.

·         Zygote undergoes cell division (mitosis) and cell differentiation.

·         Oviparous animal which lays eggs and development takes place inside egg.

·         Viviparous animal gives birth to the young. The development takes place inside the body of the female.

·         In plants:

o    Zygote developed into embryo.

o    Ovule developed into seed

o    Integument of the ovule developed into seed coat.

o    Ovary developed into fruit.

o    Ovary wall developed into pericarp.


Stages of Embryogenesis:

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