The frequency of tasters and nontasters of PTC (see Problem 10) 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.

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 phenotypic 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.