Sexual Reproduction in Animals

SEXUAL REPRODUCTION:-

When reproduction takes place as a result of fusion of male and female gametes is called sexual reproduction.

Fusion of gametes is called fertilization which results in variation.

Why the sexual mode of reproduction:-

• Sexual reproduction provides variation in DNA thereby making the offspring adapted for better survival. Sexual reproduction ensures the mixing of gene pool of the species. Due to genetic recombination, variations occur in the process of sexual reproduction.
• Reproduction incorporates such a process of combining DNA from two different individuals during reproduction.
• But this creates a major difficulty. If each new generation is to be the combination of the DNA copies from two pre-existing individuals, then each new generation will end up having twice the amount of DNA that the previous generation had.
• One solution that many multi-cellular organisms have found for the problem mentioned above is to have special lineages of cells in specialised organs in which only half the number of chromosomes and half the amount of DNA as compared to the non-reproductive body cells. This is achieved by a process of cell division called meiosis.
• When such germ cell form two individuals unite during sexual reproduction the normal chromosome number and DNA content are restored.
• In multicellular organism body design become more complex, the germ cells also specialize. One germ cell is large and contains the food stored while the other is smaller and likely to be motile. The motile germ cell is called the male gamete and the germ cell containing the stored food is called the female gamete.