Population genetics studies how genes interact and evolve through natural selection and mutations. Genetic coadaptation refers to how genes interact with each other, and linkage disequilibrium occurs when certain alleles are favored over others. This can change through random mating or if one combination results in higher fitness.
In the field of genetics, population genetics studies how often specific copies of genes, or alleles, appear and how they interact with other alleles of other genes. It also examines how evolutionary processes such as natural selection and mutations affect alleles. The distribution of alleles can be independent of other alleles in a different location or can be influenced by other alleles. When the distribution of one or more alleles is not independent of other alleles, we speak of linkage disequilibrium.
The evolution of an organism occurs through genetic variation. Different combinations of genes and different combinations of alleles of different genes lead to different phenotypes of organisms. This means that genetic variation produces organisms of one species that are similar but may look different and function differently. Genetic variation can make an organism more or less effective in terms of survival and reproduction. The theory of natural selection states that evolution occurs through the survival of the fittest, or the survival of those who are most successful in passing on their genes.
Genes are not independent units that are passed on to offspring on their own. Instead, genes are affected by the environment as well as by other genes. Genetic coadaptation is the term used to refer to how genes interact with other genes. Natural selection favors those alleles that interact well with alleles of other genes at different locations within the DNA. Genetic coadaptation can exist between alleles of some genes but not others.
For example, gene A and gene B each have two alleles, which are A1 and A2 and B1 and B2, respectively. If an organism inherits A1 and B1 or A2 and B2, it can be assumed in this example that it is better adapted to survive than if it inherits A1 and B2 or A2 and B1. This means that through natural selection, the genetic combinations of A1B1 and A2B2 would be favored as the organism with these alleles is more likely to survive and reproduce. As such, these alleles are said to be in linkage disequilibrium as they would not be randomly passed on to offspring, but instead some pairs are favored.
Linkage disequilibrium is measured by comparing allele frequencies within a population, but it is not permanent. Random mating between organisms can lead to a decrease in the presence of the related alleles. Permanent link imbalance can occur if one combination results in a higher fitness level of an organism, such as when the other combination results in a lethal mutation in a zygote. The further apart the positions of the alleles are, the more difficult it is to maintain linkage disequilibrium.
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