What Is Sexual Reproduction, Fertilization, Oviparous

SEXUAL REPRODUCTION

Asexual method of reproduction is a primitive form of reproduction than the sexual reproduction. Sexual reproduction is leading to production and union of gametes. Meiosis and genetic recombination played a major role in the development of more complex forms of life and types of gametes.

From identical gametes (isogametes) to the heterogametic stage of motile male gametes (Sperms or antherozoid) and no-motile female gametes eggs (ova).

Sexual reproduction has advantage over asexual reproduction.

Male and female differentiation:

  Both in animal and plants, evolution of sexual reproduction also lead to the differentiation of sexes (male and female). Organisms are either having one sex i.e. hermaphrodite or bisexual.

Advance mode of sexual reproduction has uni-sexuality in animals. But in plants bisexuality in general is retained. Despite the bisexuality (tape worm, earthworm etc). The cross fertilization is ensured for maintaining the advantage of genetic recombination


                                      FERTILIZATION

It is the process which leads to union of gametes. Fertilization may occur outside of the body or inside the body of the female.

External Fertilization:

External fertilization occur in aquatic environment where male gametes can swim towards the female gamete in water medium. Development is also external due to the constant stable condition of water (Forg, fish etc).

Internal Fertilization:

In terrestrial condition fertilization is internal. Sperms are lodged into the female body where fertilization occur.


                                      OVIPAROUS

In reptiles and birds, internal fertilization may lead to external development. They lay shelled eggs to protect the developing embryo from harsh terrestrial conditions. Such animals are called oviparous.

Viviparous:

In mammals, internal fertilization leads to internal development and development of embryo is accomplished inside the female body, which give birth to young one-such animals are called viviparous.

Ova-viviparous:

In some mammals like Duckbill platypus (arachnids), internal fertilization lead to internal development of the young one in a shelled egg and when development completed , shelled egg is laid which hatched the offspring. This is called ova-viviparous condition.

Protective view:

viviparous and ova-viviparous animal provide more protection to their young one during development. Nourishment is provided either through stored food in the egg or through placenta by the mother.