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%. Calculate the frequency of the dominant (T) allele for PTC tasting and the recessive (t) allele for nontasting in each population.

Key Concepts

Hardy-Weinberg Principle

The Hardy-Weinberg Principle provides a mathematical framework for understanding allele frequencies in a population. It states that allele and genotype frequencies will remain constant from generation to generation in the absence of evolutionary influences. This principle is essential for calculating allele frequencies, as it allows us to relate the observed phenotypic ratios to the underlying genotypic ratios.

Allele Frequency Calculation

Allele frequency refers to how often a particular allele appears in a population. For a trait governed by a dominant (T) and recessive (t) allele, the frequencies can be calculated using the phenotypic proportions. For example, if 64% of a population are tasters (TT or Tt), we can use this information to derive the frequencies of the T and t alleles using the Hardy-Weinberg equations.

Autosomal Dominance

Autosomal dominance is a pattern of inheritance where only one copy of a dominant allele is needed for the trait to be expressed. In the case of PTC tasting, the T allele is dominant over the t allele. Understanding this concept is crucial for interpreting the phenotypic ratios in the populations and for calculating the corresponding allele frequencies accurately.