Explain how sexual reproduction gives rise

solution:
Variations occurring during sexual reproduction may be due to :

(i) Separation of homologous chromosomes (by chance only) during gamete formation,

(ii) Crossing over (recombination) of homologous chromosomes.

(iii) Fertilisation of gametes to form zygote.

(iv) Errors during DNA copying or mutations.

In asexually reproducing organisms errors during DNA copying cause variations.

Since the extent of variations is much larger in sexually reproducing organisms therefore, the chances of evolution is also much higher in sexually reproducing organisms.

These variation enables the organism to adapt themselves to the changing conditions and also help to face the struggle for existence. Over the time, they accumulate and give rise to new species.