Introduction: Sexual reproduction is a process that involves the fusion of two gametes to form a zygote. This process is favoured under certain conditions due to its advantages over asexual reproduction.

Genetic Variability: Sexual reproduction leads to genetic variability in offspring which is crucial for the survival of a species. This is because genetic variation increases the likelihood of some individuals possessing traits that are favourable for survival in a changing environment.

Adaptability: Sexual reproduction facilitates adaptation to changing environments. In asexual reproduction, offspring are identical to the parent, and any changes in the environment may lead to the extinction of the entire population. However, sexual reproduction produces offspring with varying traits, and some may be better adapted to changing environments.

Resistance to Diseases: Sexual reproduction provides better resistance to diseases. The genetic variability resulting from sexual reproduction enables the production of offspring with resistance to diseases. This is because some individuals may possess genes that offer better resistance to diseases, and these genes can be passed on to their offspring.

Elimination of Harmful Mutations: Sexual reproduction enables the elimination of harmful mutations. Harmful mutations may arise during the formation of gametes, and sexual reproduction allows for the elimination of such mutations through the fusion of gametes from different individuals.

Conclusion: Sexual reproduction is favoured under certain conditions due to its advantages over asexual reproduction. These advantages include genetic variability, adaptability to changing environments, resistance to diseases, and elimination of harmful mutations.

Organisms such as fungi and algae switch to sexual mode of reproduction during adverse conditions because sexual reproduction brings variation into the individuals, some of which might help the individuals to adapt to the changed conditions and survive. This ensures the continuity of species