Calculating Allele Frequency from Genotype Data: Worked Examples

🧬 Quick Study Guide

• 🔢 Allele frequency is the proportion of an allele within a population.
• 📝 Genotype frequency is the proportion of a genotype (e.g., AA, Aa, aa) within a population.
• 🔑 Key Formulas:
  • $p = \text{frequency of allele A}$
  • $q = \text{frequency of allele a}$
  • $p + q = 1$
  • For a diploid organism: $p = \frac{\text{number of A alleles}}{\text{total number of alleles}}$
• 💡 Hardy-Weinberg Equilibrium provides a baseline for expected genotype frequencies: $p^2 + 2pq + q^2 = 1$, where:
  • $p^2$ is the frequency of AA
  • $2pq$ is the frequency of Aa
  • $q^2$ is the frequency of aa
• 🧮 To calculate allele frequencies from genotype data:
  1. Count the number of each genotype (AA, Aa, aa).
  2. Calculate the total number of alleles in the population (2 times the number of individuals).
  3. Calculate the number of each allele (A and a).
  4. Divide the number of each allele by the total number of alleles.

🧪 Practice Quiz

1. In a population of 500 individuals, 20 are homozygous dominant (AA), 180 are heterozygous (Aa), and 300 are homozygous recessive (aa). What is the frequency of the 'a' allele?

   1. 0.34
   2. 0.59
   3. 0.69
   4. 0.74

2. If the frequency of the 'A' allele is 0.6, what is the frequency of the 'a' allele, assuming only two alleles exist for this gene?

   1. 0.16
   2. 0.24
   3. 0.4
   4. 0.6

3. In a population, the frequency of the homozygous recessive genotype (aa) is 0.09. Assuming Hardy-Weinberg equilibrium, what is the frequency of the 'a' allele?

   1. 0.03
   2. 0.3
   3. 0.81
   4. 0.91

4. In a population of 1000 individuals, 360 are of genotype MM, 480 are MN, and 160 are NN. What is the frequency of the M allele?

   1. 0.36
   2. 0.48
   3. 0.6
   4. 0.72

5. If the frequency of the heterozygous genotype (Aa) is 0.48 and the population is in Hardy-Weinberg equilibrium, and the frequency of A is greater than a, what is the frequency of the 'A' allele?

   1. 0.2
   2. 0.4
   3. 0.6
   4. 0.8

6. A population of butterflies has two color forms: yellow (YY or Yy) and white (yy). If 400 out of 1000 butterflies are white, what is the frequency of the 'y' allele, assuming Hardy-Weinberg equilibrium?

   1. 0.2
   2. 0.4
   3. 0.6
   4. 0.8

7. In a certain population, 16% of individuals express the recessive phenotype. Assuming Hardy-Weinberg equilibrium, what percentage of the population would you expect to be heterozygous?

   1. 16%
   2. 24%
   3. 48%
   4. 84%