Biology - Reproduction in Animals


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Introduction

  • Reproduction is the most essential for the continuation of a species.

  • Reproduction ensures the continuation of similar kinds of species, generation after generation.

Modes of Reproduction

  • Following are the two modes of reproduction −

    • Sexual reproduction

    • Asexual reproduction

  • Let us discuss each one separately −

Sexual Reproduction

  • In animals, males and females have different reproductive organs.

  • The reproductive parts in animals produce gametes that fuse and form a zygote.

  • The zygote develops into a new similar species.

  • The type of reproduction through the fusion of male and female gametes is known as sexual reproduction.

  • The male gametes, produced by testes, are known as sperms.

  • The female gametes, produced by ovary, are known as ova (or eggs).

  • In the process of reproduction, the first step is the fusion of a sperm and an ovum (egg).

Fertilization
  • Fusion of the egg and the sperm is known as fertilization (as shown in the above image).

  • During the fertilization, the nuclei of the sperm and the egg fuse together and form a single nucleus that result into the formation of a fertilized egg also known as zygote (shown in the image given below).

Zygote
  • The zygote further divides repeatedly to give rise to a ball of cells that begin to form groups. The groups develop into different tissues and organs constituting a full body. In the process, the developing structure is known as an embryo (shown in the image given below).

Embryo Development
  • The embryo continues to develop in the uterus and develops body parts such as head, face, ear, eyes, nose, hands, legs, toes, etc.

  • The stage of the embryo in which different parts of the body develop and can be identified is known as foetus (shown in the image given below).

Foetus in Uterus
  • In a defined period of time, when the development of the foetus is complete, the mother gives birth to the baby.

  • The animal which gives birth to young ones is known as viviparous animal. E.g. Human, cow, dogs, etc.

  • The organism that lays eggs is known as oviparous animal. E.g. all birds (except bats), lizard, etc.

Asexual Reproduction

  • The type of reproduction in which only a single parent, gets divided into two new offspring, is known as asexual reproduction. E.g. Hydra and Amoeba.

  • In hydra, the individuals develop from the buds; therefore, this type of asexual reproduction is known as budding (shown in the image given below).

Hydra
  • In amoeba, nucleus gets divided into two nuclei; therefore, such kind of asexual reproduction is known as binary fission.

Amoeba Fission

Cloning

  • Cloning is the modern science technique to produce an exact copy of a cell, any other living part, or a complete organism.

  • For the first time, cloning of an animal was successfully performed by Ian Wilmut and his colleagues at the Roslin Institute in Edinburgh, Scotland.

  • In 1996, they cloned successfully a sheep and named that Dolly.

Dolly

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