![]() But for many populations this is not the case. One of the assumptions of the Hardy-Weinberg Law is that the population is closed. Many important genes such as hemoglobin and muscle genes in humans, and seed storage and photosynthetic genes in plants are organized as multigene families. This type of evolution generates multigene families. With this adaptive constraint removed, further changes can occur that generate a new gene that has a similar function in the organism, but may function at a specific time in development, or in a unique location in the individual. If a single gene that is important undergoes a duplication, mutation in the duplicated copy would not necessarily reduce the fitness of the individual because it still would have a functioning copy of the original gene. But the genome of a species can undergo another type of change, gene duplication, which actually favors mutational events. Mutations are generally deleterious and are selected against. The most basic type of mutation is the change in a single nucleotide in the gene. If the mutation is beneficial to the species as a whole, migration from the population in which it initially arose must occur for it to spread to other populations of the species. But if the environment changes, then the new mutant allele may be favored and eventually become the dominant alelle in that population. Most of these mutations though will be detrimental and lost. Alternatively, the mutation could generate an entirely new allele. The mutation could be a change in one allele to resemble one currently in the population, for example from a dominant to a recessive allele. If fitness is improved by a mutation, then frequencies of that allele will increase from generation to generation. Harmful mutations will be lost if they reduce the fitness of the individual. Mutations are classified as beneficial, harmful or neutral. The three primary methods of change are mutation, migration and selection. Clearly the population had evolved to a higher adaptive condition.īecause population changes require changes in gene frequencies, it is important to understand how these frequencies can change. ![]() In its place, the dark-colored allele became the most predominant allele because moths that carried that allele could camouflage themselves on the stained trees and avoid being eaten by their bird predators. Gradually the light-colored moth was attacked and that allele became much less prevalent. But the pollution generated by the new industries stained the light-colored trees dark. The light-colored moths would hide on the white-barked trees and avoid bird predation. Prior to the industrialization of central England, the light-colored allele was most prevalent. The moth can be either dark or light colored. The classic example which supports this theory is that of the peppered moth in England. Selection will then chose the better adapted individuals, and the population will have evolved. Several factors such as mutation of alleles and migration of individuals with those new alleles will create variation in the population. This theory states that a species evolves when gene frequencies changes and the species moves it to a higher level of adaptation for a specific ecological niche. The synthetic theory of evolution as described by Sewell Wright attempts to explain evolution in terms of changes in gene frequencies. Consequently the gene frequencies will change and the population will evolve. The distribution will change because genotypes in the subsequent generation will not appear in direct relationship to the gene frequencies of that population prior to the change. By altering the fitness of an individual, the mating distribution will change. Viability and fertility are traits that are associated with fitness and are directly related to the ability of an individual to survive long enough to reproduce. Several factors can act to change fitness. The Hardy-Weinberg Law described a population that exists in genetic equilibrium. Population and Evolutiionary Genetics WWW Linksīecause a genetic population is described as the sum of gene (or allelic) frequencies for all the genes represented by that population, it follows that for evolution of a species to occur the gene frequencies of that population must undergo change. Population and Evolutiionary Genetics Overheads Deriving Genotypic and Allelic Frequencies
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