Final answer:
Selective breeding of animals and plants by humans can decrease genetic diversity by favoring certain traits and reducing the occurrence of others. This can lead to a reduced overall genetic diversity within a population.
Step-by-step explanation:
Selective breeding of animals and plants by humans can affect genetic diversity in several ways. By intentionally breeding individuals with desired traits, humans can increase the frequency of those traits in the population and decrease the frequency of other traits. Over time, this can lead to a reduced overall genetic diversity within a population. Additionally, selective breeding can lead to the creation of new breeds or varieties, further reducing the genetic diversity within a species.