The evolution of a population of a species is affected by whether the individual organisms reproduce sexually or asexually.
Sexual reproduction involves the fusion of the nuclei of a male and female sex cell during fertilisation. The offspring inherit a mixture of alleles from both parents.
In asexual reproduction an exact genetic copy of the parent organism is produced (a clone).
Unlike sexual reproduction, asexual reproduction only introduces genetic variation into the population if a random mutation in the organism's DNA is passed on to the offspring.
Bacteria, such as E. coli, reproduce asexually. An advantage of this is that they can produce many bacteria very quickly. A disadvantage is that all of the bacteria are genetically identical. If an antibiotic was put on the bacteria, then all of them would die. The population would be wiped out. The only way for variation to be introduced into the population is by random mutation.
Most animals reproduce sexually, for example, rabbits. The process of sexual reproduction introduces variation into the species because the alleles that the mother and the father carry are mixed together in the offspring. A disadvantage is that sexual reproduction takes longer than asexual reproduction. A mate must be found, the egg must be fertilised by sperm, and then the offspring develop. The benefit of introducing genetic variation into the species, however, outweighs this disadvantage. If a disease were to hit the rabbit population, then perhaps not all of the rabbits would be affected because of the variation in the population. This means that some individuals would survive to be able to reproduce and generate more offspring.