Final answer:
The tendency for like individuals to mate is called positive assortative mating, which affects the genetic structure of a population by increasing certain traits. Inbreeding, on the other hand, can lead to harmful phenotypes due to the combination of deleterious mutations, which is why breeders discourage mating between close relatives.
Step-by-step explanation:
The tendency for like individuals to mate is known as positive assortative mating. Assortative mating is an individual's preference to mate with partners who are phenotypically similar to themselves. This form of mating can impact the genetic structure of a population by increasing the prevalence of certain traits over time.
In contrast, inbreeding is the mating of closely related individuals, which can lead to inbreeding depression, manifested as an increase in abnormalities and diseases in the population. Inbreeding can bring together rare deleterious mutations that can lead to harmful phenotypes, thereby often resulting in offspring that are not as fit as those from two unrelated individuals.
One of the effects of nonrandom mating is that it can change the population. Natural selection then acts on these traits, further shaping the genetic landscape of the species. Notably, this can lead to adaptive evolution, where beneficial alleles increase in frequency and deleterious alleles decrease due to selection.