Variation and Sexual Reproduction

• Costs and benefits of sexual and asexual reproduction Costs of sexual reproduction: males unable to produce offspring; only half of each parent’s genome passed onto offspring, disrupting successful parental genomes
• Benefits outweigh costs due to an increase in genetic variation in the population
• Genetic variation provides the raw material required for adaptation, giving sexually reproducing organisms a better chance of survival under changing selection pressures
• The Red Queen hypothesis to explain the persistence of sexual reproduction
• Co-evolutionary interactions between parasites and hosts may select for sexually reproducing hosts
• If hosts reproduce sexually, the genetic variability in their offspring reduces the chances that all will be susceptible to infection by parasites
• Asexual reproduction can be a successful reproductive strategy as whole genomes are passed on from parent to offspring
• Maintaining the genome of the parent is an advantage particularly in very narrow, stable niches or when re-colonising disturbed habitats
• Vegetative cloning in plants and parthenogenesis in lower plants and animals that lack fertilisation are examples of asexual reproduction in eukaryotes
• Offspring can be reproduced more often and in larger numbers with asexual reproduction
• Parthenogenesis is more common in cooler climates, which are disadvantageous to parasites, or regions of low parasite density or diversity
• Asexually reproducing populations are not able to adapt easily to changes in their environment, but mutations can occur that provide some degree of variation and enable some natural selection and evolution to occur
• Organisms that reproduce principally by asexual reproduction also often have mechanisms for horizontal gene transfer between individuals to increase variation, for example the plasmids of bacteria and yeasts