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Find p. The sum of the frequencies of both alleles = 100%, p + q = l. You know q, so what is p, the frequency of the dominant allele?

.5

Find 2pq. The frequency of the heterozygotes is represented by 2pq. This gives you the percent of the population that is heterozygous for white coat:

50%

The Hardy-Weinberg equation is useful for predicting the percent of a human population that may be heterozygous carriers of recessive alleles for certain genetic diseases. Phenylketonuria (PKU) is a human metabolic disorder that results in mental retardation if it is untreated in infancy. In the United States, one out of approximately 10,000 babies is born with the disorder. Approximately what percent of the population are heterozygous carriers of the recessive PKU allele?

Answer: Approximately 2% of the U.S. population carries the PKU allele. Calculation: q2 = 1/10,000 = 0.0001 q = √0.0001 = 0.01 p = 1 − q = 1 − 0.01 = 0.99 The carriers are heterozygous. Therefore, 2pq = 2 (0.99) (0.01) = 0.0198 = 1.98%

Calculate q2. Count the individuals that are homozygous recessive in the illustration above. Calculate the percent of the total population they represent. This is q2.

Answer: Four of the sixteen individuals show the recessive phenotype, so the correct answer is 25% or 0.25.

In a certain population of 1000 fruit flies, 640 have red eyes while the remainder have sepia eyes. The sepia eye trait is recessive to red eyes. How many individuals would you expect to be homozygous for red eye color? Hint: The first step is always to calculate q2! Start by determining the number of fruit flies that are homozygous recessive. If you need help doing the calculation, look back at the Hardy-Weinberg equation.

Answer: You should expect 160 to be homozygous dominant. Calculation: q2 for this population is 360/1000 = 0.36 q = √0.36 = 0.6 p = 1 − q = 1 − 0.6 = 0.4 The homozygous dominant frequency = p2 = (0.4)(0.4) = 0.16. Therefore, you can expect 16% of 1000, or 160 individuals, to be homozygous dominant.

If you are told that the frequency of a recessive allele in a population is 10%, you are directly given q, since by definition q is the frequency of the recessive allele. This comprises all the copies of the recessive allele that are present in heterozygotes as well as all the copies of the allele in individuals that show the recessive phenotype. What is q for this population?

Answer: q = 0.1

Find q. Take the square root of q2 to obtain q, the frequency of the recessive allele.

Answer: q = 0.5

If you observe a population and find that 16% show the recessive trait, you know the frequency of the aa genotype. This means you know q2. What is q for this population?

Answer: q is the square root of 0.16 = 0.4