Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually ? [CBSE 2011,2014]

During sexual reproduction there is ‘crossing over’ of chromosomes, that gives rise to variations. These variations are inherited and increase the chances of survival of an organism. In sexual reproduction variations may occur due to errors in DNA copying. There may be variations due to interchange of homologous chromosomes during crossing over of male and female. In sexual reproduction, it is not predetermined that which gamete would fuse with another gamete. It depends only on chance. It is also a reason of variation. These variations enable the organisms to adapt themselves to the changing conditions and also help to give rise to new species.