The frequency of tasters and nontasters of PTC varies among populations. In population A, 64% of people are tasters (an autosomal dominant trait) and 36% are nontasters. In population B, tasters are 75% and nontasters 25%. In population C, tasters are 91% and nontasters are 9%.
Assuming that Hardy–Weinberg conditions apply, determine the genotype frequencies in each population.

Verified step by step guidance

1. Start by recalling the Hardy-Weinberg principle, which states that the genotype frequencies in a population can be represented as p² (homozygous dominant), 2pq (heterozygous), and q² (homozygous recessive), where p is the frequency of the dominant allele and q is the frequency of the recessive allele. Also, p + q = 1.
2. For each population, identify the frequency of nontasters (q²), as nontasting is the recessive trait. For example, in population A, q² = 0.36, in population B, q² = 0.25, and in population C, q² = 0.09.
3. Calculate q (the frequency of the recessive allele) for each population by taking the square root of q². For example, q = √q².
4. Determine p (the frequency of the dominant allele) for each population using the equation p + q = 1. Solve for p by subtracting q from 1.
5. Finally, calculate the genotype frequencies for each population: p² (homozygous dominant), 2pq (heterozygous), and q² (homozygous recessive). Use the values of p and q obtained in the previous steps to compute these frequencies using the formulas p² = p × p, 2pq = 2 × p × q, and q² = q × q.

Key Concepts

Hardy-Weinberg Principle

The Hardy-Weinberg Principle is a fundamental concept in population genetics that describes how allele and genotype frequencies remain constant from generation to generation in a population under certain conditions. These conditions include a large breeding population, random mating, no mutation, no migration, and no natural selection. This principle provides a baseline to compare actual genetic variation in populations.

Autosomal Dominance

Autosomal dominance refers to a pattern of inheritance where only one copy of a dominant allele is necessary for the expression of a trait. In the case of PTC tasting, the ability to taste is dominant, meaning individuals with at least one dominant allele (T) will be tasters, while those with two recessive alleles (tt) will be nontasters. Understanding this concept is crucial for calculating genotype frequencies based on phenotype ratios.

Genotype Frequencies

Genotype frequencies represent the proportion of different genotypes in a population. In the context of the Hardy-Weinberg equation, these frequencies can be calculated using the allele frequencies. For a trait with two alleles, the frequencies of homozygous dominant (TT), heterozygous (Tt), and homozygous recessive (tt) genotypes can be derived from the overall frequency of the dominant and recessive phenotypes, allowing for predictions about genetic variation in populations.