Q.
It is observed that simple organisms like algae and fungi normally reproduce asexually but before the onset of adverse conditions they shift to sexual reproduction. It is so because sexual reproduction
During favourable conditions, simple organisms like algae and fungi multiply asexually but during unfavourable conditions gametes are formed. The gametes fuse to form zygote which often develops a thick wall to become zygospores. The later is dispersed. Under favourable conditions zygospore germinates to form new organism. Since fusion of gametes from diferent parents occur during sexual reproduction, hence genetic recombination takes place causing variations. Variations, being a major factor of natural selection, play an important role in evolution.