New genetic variation is produced in populations of organisms that can reproduce sexually by recombination and in individuals by gene and chromosome mutations. The pool of genetic variation present in an interbreeding population is shaped by selection. Selection leads to certain genetic attributes being preferred and results in changes to the frequency of genes within this pool. Thus it can be seen that chromosomes play a major role in genetic diversity. Sexual selection and sexual determination are two topics to consider when dealing with genetics.
Sexual selection is an important part of the evolution of most vertebrate species.
Pacific salmon come to spawn once in their life, and this period is very intense. The spawning period is very precise, and takes from a large group of salmon, specific salmon that are the most effective breeders, hence the name breeding competition. Unfortunately, in hatcheries, this process is overlooked. It is almost certain that this results in salmon that have a loss of general vigor, adaptation to local environments, and evolutionary fitness. A subtopic of sexual determination is the sex ratio.