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Sample Hardy-Weinberg Problems – Answers 1. In a population of 100 individuals 49% are of the NN blood type. What percentage is expected to be MN assuming Hardy-Weinberg equilibrium? A. 9% B. 21% C. 42% D. 51% E. insufficient information to answer question Reason: q 2 = 49% or .49, so q = .7 p=.3. The genotype MN is heterozygous so the frequency = 2pq = 2(.3)(.7) = 42% 2. Attached ears is an autosomal recessive trait in humans. Assume that there are 400 people with attached ears in a population of 10000. How many individuals would be expected to homozygous dominant? A. 800 B. 100 C. 6400 D. 200 E. 10,000 Reason: People with attached ears are homozygous recessive (ee). Therefore, the frequency of people with attached ears = 400/10000 = .04 = q 2 , so q = .2. Therefore, p = .8. The frequency of homozygous dominant individuals (EE) = p 2 = (.8) 2 = .64. The total expected number of people = .64 * 10000 = 6400 people. 3. In a population that meets the H-W equilibrium assumptions, 81% of the individuals are homozygous for a recessive gene. What percentage of the individuals would be expected to be heterozygous for this gene in the next generation? Answer: 81% of people are homozygous recessive. q 2 = .81, so q = .9 and p = .1. Therefore, the expected percentage of heterozygous individuals = 2pq = 2(.1)(.9) = .18 or 18%. Notice, this is an example where the recessive allele is more common than the dominant allele. Remember, the terms "dominant" and "recessive" are terms that refer only to the relationship to the alleles and whether they are expressed or not in the heterozygote. There are many examples of genes where the recessive allele is more common in the population. 4. Coat color in a population of rabbits is controlled by three alleles. The c+ allele codes for brown coat, the cch allele codes for chinchilla coloration, and the ch allele codes for himalayan coloration. The dominance relationship is c+ > cch > ch. Suppose that in a population of 100 rabbits there were 4 himalayans and the frequency of the chinchilla allele is .20.

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What are the frequencies of the 3 alleles? Answer: The 4 himalayans are homozygous recessive. Therefore, r
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