Factors causing changes in allele and genotype frequencies
Genetics
Please explain one of the following:
1) What factors can cause changes in allele frequencies and genotype frequencies?
The allele frequency represents the incidence of a gene variant in a population. Alleles are variant forms of a gene that are located at the same position, or genetic locus, on a chromosome. An allele frequency is calculated by dividing the number of times the allele of interest is observed in a population by the total number of copies of all the alleles at that particular genetic locus in the population. Allele frequencies can be represented as a decimal, a percentage, or a fraction.
In a population, allele frequencies are a reflection of genetic diversity. Changes in allele frequencies over time can indicate that genetic drift is occurring or that new mutations have been introduced into the population.
2) What is the Hardy-Weinberg equilibrium, and how do we use their formula?
The Hardy–Weinberg Principle
The Hardy–Weinberg principle relates allele frequencies to genotype frequencies in a randomly mating population. Imagine that you have a population with two alleles (A and B) that segregate at a single locus. The frequency of allele A is denoted by p and the frequency of allele B is denoted by q.
The Hardy–Weinberg principle states that after one generation of random mating genotype frequencies will be p2, 2pq, and q2. In the absence of other evolutionary forces (such as natural selection), genotype frequencies are expected to remain constant and the population is said to be at Hardy–Weinberg equilibrium. The Hardy–Weinberg principle relies on a number of assumptions: (1) random mating (i.e, population structure is absent and matings occur in proportion to genotype frequencies), (2) the absence of natural selection, (3) a very large population size (i.e., genetic drift is negligible), (4) no gene flow or migration, (5) no mutation, and (6) the locus is autosomal. When these assumptions are violated, departures from Hardy–Weinberg proportions can result.