Hardy-Weinberg practice

  1. Hardy-Weinberg tutorial (allele frequencies):

  2. If 98 out of 200 individuals in a population express the recessive phenotype, what percent of the population are homozygous dominant?
    1. 49% (wrong)
    2. 70% (wrong)
    3. 30% (wrong)
    4. 42% (wrong)
    5. 9% <==== correct
    Solution:
    • Recessive phenotype implies homozygous genotype. q2 = 98 / 200 = 0.49
    • q = 0.7
    • p + q = 1
    • p + 0.7 = 1
    • p = 0.3
    • p2 = 0.32 = 0.09


  3. If 98 out of 200 individuals in a population express the recessive phenotype, what percent of the population are heterozygotes?
    1. 49% (wrong)
    2. 70% (wrong)
    3. 30% (wrong)
    4. 42% <==== correct
    5. 9% (wrong)
    Solution:
    • Recessive phenotype implies homozygous genotype. q2 = 98 / 200 = 0.49
    • q = 0.7
    • p + q = 1
    • p + 0.7 = 1
    • p = 0.3
    • 2pq = 2 (0.7 * 0.3) = 0.42
    • double check: p2 + 2pq + q2 = 1?
    • double check: 0.09 + 0.42 + 0.49 = 1.

    Brown hair (B) is dominant to blond hair (b). If there are 168 brown hairs in a population of 200:


  4. What is the predicted frequency of heterozygotes?
    1. 16% (wrong)
    2. 40% (wrong)
    3. 60% (wrong)
    4. 48% <==== correct
    5. 84% (wrong)
    Solution:
    • BB + Bb = 168 / 200 = 0.84 = brown hairs
    • bb = 1 - 0.84 = 0.16 = q2 blond hairs
    • q = 0.4
    • p = 1 - q = 1 - 0.4 = 0.6
    • 2pq = 2 (0.4 * 0.6) = 0.48


  5. What is the predicted frequency of homozygous dominant?
    1. 16% (wrong)
    2. 40% (wrong)
    3. 60% (wrong)
    4. 48% (wrong)
    5. 36% <==== correct
    Solution:
    • p2 = 0.62 = 0.36


  6. What is the predicted frequency of homozygous recessive?
    1. 16% <==== correct
    2. 40% (wrong)
    3. 60% (wrong)
    4. 48% (wrong)
    5. 36% (wrong)
    Solution:
    • q2 = 0.42 = 0.16

    • double check: p2 + 2pq + q2 = 1?
    • double check: 0.62< + 2 (0.6 * 0.4) + 0.42 = 0.36 + 0.48 + 0.16 = 1.

    If blonds occur in 36% of the population:


  7. What is the allele frequency for b?
    1. 36% (wrong)
    2. 60% <==== correct
    3. 40% (wrong)
    4. 16% (wrong)
    5. 48% (wrong)
    Solution:
    • bb = q2 = 0.36
    • q = b = 0.6


  8. What is the allele frequency for B?
    1. 36% (wrong)
    2. 60% (wrong)
    3. 40% <==== correct
    4. 16% (wrong)
    5. 48% (wrong)
    Solution:
    • p + q = 1
    • p + 0.6 = 1
    • q = 1 - 0.6 = 0.4


  9. What is the predicted frequency of heterozygotes?
    1. 36% (wrong)
    2. 60% (wrong)
    3. 40% (wrong)
    4. 16% (wrong)
    5. 48% <==== correct
    Solution:
    • 2pq = 2 (0.6 * 0.4) = 0.48


  10. What is the predicted frequency of homozygous dominant?
    1. 36% (wrong)
    2. 60% (wrong)
    3. 40% (wrong)
    4. 16% <==== correct
    5. 48% (wrong)
    Solution:
    • p2 + 2pq + q2 = 1
    • p2 + 0.48 + 0.36 = 1
    • p2 = 1 - (0.48 + 0.36)
    • p2 = 1 - 0.84
    • p2 = 0.16