Question

Hardy-Weinberg
a. if you know allelic frequencies for a particular gene in your class, can you calculate phenotypic frequencies. why or why not

b. if you know allelic frequencies for a population, can you always calculate phenotypic frequencies.

c. if the fraction of homozygous recessive in a population is known, can the allelic frequencies and genotypic frequencies always be calculated? what conditions must be met?

Answer 1

The Hardy-Weinberg law states that the proportions or frequencies of the alleles in gene pool of a population remain constant or at equilibrium from generation to generation unless acted upon by agents other than sexual recombination. The genotypic frequencies stabilize after one generation in proportions determined by allelic frequencies. The Hardy-Weinberg equation provides a standard to measure the changes in allele frequencies occurring in the natural populations without this equation the change in the frequency of alleles the magnitude and direction of the alleles and the forces responsible for change in allele characteristics can not be detected.

a) Yes. When allelic frequencies of a particular gene is known, the genotype frequency is known and the genotype frequency is relavant to the phenotypic frequency. For example, allele encoding Phenylthiocarbamide(PTC) results in bitter taste. Some people perceive the taste whiole others are not. The tasting ability depends on genotype of individuals. The individuals with genotype encoding two dominant alleles for PTC or heterozygous genotype with one dominant and one recessive results in individuals able to taste PTC. The individuals with two recessive alleles cannot taste PTC.

b) Yes. When allele frequency of a gene is known then the phenotypic frequencies can be calculated with help of genotype frequency.

c) When homozygous recessive fraction in a population is given, the frequency of recesive genotype and allele is calculated. The dominant allele frequency can be calculated using equation p= 1- q. For calculation of frequency of either of alleles, the conditions should meet include the population must be in equilibrium and frequencies of alleles should be equal to 1. The Hardy Weinberg equilibrium is determined with equation used to calculate allele frequencies and the equation is (p²+2pq+q² = 1).