Recap: What is Genetic Drift?
Individuals show variation in their genotype. Chance dictates what alleles get pass on. By chance, there may be a more common allele being passed on which can lead to evolution. Genetic drift will have a larger affect on smaller populations as chance has greater influence. For example 8/10 or 8/100, both equivalent frequencies but over a different sized population, 8 has a larger effect on the smaller population. In larger populations, chance variations tend to even out across population. Natural selection and genetic drift work together to cause evolution.
An example of genetic drift: Blood group within Native American tribes
Different blood groups arise, as there is no selection pressure involving this phenotype, it does not involve natural selection. By chance, certain blood groups have become more common.
Genetic bottlenecks are large events which cause a mass reduction in population size, for example a natural disaster occurrence. If a huge tsunami wiped out a large sum of the total population then in the remaining population something may become more common due to genetic drift.
What is the Founder Effect?
This is where a small population start a new population. Initially the gene pool is rather small. However, there is variation in genotypes between organisms and by chance most organisms share same genotypes. Without further gene flow, there will be little genetic variation and therefore the population will be heavily influenced by genetic drift. It is important to remember genetic drift has a heavy effect on the founder effect.
Examples of where the founder effect has occurred:
The Amish are a group of traditionalist Christian church fellowships which live in America, and originate from Switzerland. They adopted a simple form of life, and do not associate themselves with people from outside the group. As a result, the gene pool is small, there is little genetic diversity and little gene flow. This leads to a high incidence of genetic disorders.
The Fugates of Kentucky are a family that lived in the hills of Kentucky. The remote area resulted in a very high level of consanguinity in marriage between family. A recessive allele spread, which caused blue skin.
The Hardy-Weinberg principle is used to calculate allele frequencies in populations . The principle predicts that allele frequencies of a population will not change from one generation to the next. But, the principle is only true under the conditions that, there is no immigration, emigration, mutation or natural selection, and there is a need for random mating (all possible genotypes can breed with all others.) The equation is based on the principle and is used to estimate the allele frequencies and genotype frequencies of a population.
The equation is:
where p is the dominant allele frequency and q is the recessive allele frequency.
p2 +2pq+ q2 = 1
where p suared is homozygous dominant genotype frequency, 2pq is heterozygous genotype frequency and q squared is homozygous recessive genotype frequency
What is speciation?
Speciation is the development of a new species, caused by reproductive isolation of a species. Changes in allele frequencies cause change in phenotypes so the two groups can no longer successively breed together.