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 and Canada had a small number of founders.Deriving Genotypic and Allelic Frequencies An example is described in the Figure below.įounder Effect in the Amish Population. By chance, allele frequencies of the founders may be different from allele frequencies of the population they left. Founder effect occurs when a few individuals start, or found, a new population.By chance, allele frequencies of the survivors may be different from those of the original population. This might happen because of a natural disaster such as a forest fire. Bottleneck effect occurs when a population suddenly gets much smaller.They are called bottleneck effect and founder effect. There are two special conditions under which genetic drift occurs. In this way, allele frequencies may drift over time. In a small population, you may also, by chance, get different allele frequencies than expected in the next generation. If you toss a coin just a few times, you may, by chance, get more or less than the expected 50 percent heads or tails. When a small number of parents produce just a few offspring, allele frequencies in the offspring may differ, by chance, from allele frequencies in the parents. Genetic drift is a random change in allele frequencies that occurs in a small population.
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