USA Biology Olympiad (USABO) Practice Exam

In a population of flowers in Hardy-Weinberg equilibrium, what would be the frequency of heterozygotes if the red allele is dominant?

1. 0.1

2. 0.25

3. 0.48

4. 0.75

The correct answer is: 0.48

In a population in Hardy-Weinberg equilibrium, the frequencies of the genotypes can be determined using the allele frequencies. When dealing with one dominant allele (in this case, the red allele) and one recessive allele, let’s denote the frequency of the dominant allele (red) as "p" and the frequency of the recessive allele as "q." The sum of these frequencies must equal 1, so p + q = 1. The genotype frequencies can be described as follows: - Homozygous dominant (red/red): p² - Heterozygous (red/white): 2pq - Homozygous recessive (white/white): q² Since the question does not provide specific allele frequencies, we can analyze the case of heterozygotes, which is given by the term 2pq. To achieve frequency values like those in the answer choices, we can assume various allele frequencies and calculate the heterozygous frequency for these scenarios. Let’s consider a situation where p and q are equal, which often provides a point of reference in populations for theoretical exercises. If we assume p = 0.5 (the frequency of the dominant red allele) and q = 0.