Question 21 1 pts Tay-Sachs disease affects in 1 in 3,600 Ashkenazim births. The value of $q^2$ is • 0.05 0.1 • 0.0003 ? 0.017
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Step 1: The frequency of the Tay-Sachs disease is 1/3600. Show more…
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Population: 10,000. 36 infants are homozygous recessive for Tay Sachs disease. This rare autosomal recessive genetic disorder is found in the highest frequency among Jews from Eastern Europe and is lethal within the first two years of life. To answer the following questions, you will need to use the Hardy-Weinberg equations: p + q = 1.0 and p^2 + 2pq + q^2 = 1.0. T is the dominant allele, which codes for the normal condition, while t is the recessive allele, which codes for the Tay Sachs condition. How many individuals will NOT exhibit (phenotypically) Tay Sachs in this population? a) 9964 b) 9400 c) 1128 d) 600
Madhur L.
Tay-Sachs disease is an autosomal recessive neurological disorder that is fatal in infancy. Despite its invariably lethal effect, Tay-Sachs disease occurs at a very high frequency in some Central and Eastern European (Ashkenazi) Jewish populations. In certain Ashkenazi populations, 1 in 500 infants has Tay-Sachs disease. Population biologists believe the high frequency is a consequence of genetic bottlenecks caused by pogroms (genocide) that have reduced the population multiple times in the last several hundred years. Part 1: In the population described, what is the frequency of the recessive allele that produces Tay-Sachs disease? Express your answer using three decimal places. Part 2: Assuming mating occurs at random in this population, what is the probability that a couple are both carriers of Tay-Sachs disease? Express your answer using three decimal places.
Sri K.
Tay-Sachs disease is an autosomal recessive disorder. Among Ashkenazi Jews, the frequency of Tay-Sachs disease is 1 in 3600. If the Ashkenazi population is mating randomly, what proportion of the population consists of heterozygous carriers of the Tay-Sachs allele? First, we need to go through this question and identify what information has been given to us. Since the disease is an autosomal recessive disorder, we know all affected individuals are aa. What are we being asked to find? The frequency of carriers. What is the genotype of a carrier for a recessive disorder? Since the population is presumably large (3600+ individuals) and randomly mating, we can use the frequency of the aa genotype (affected individuals) to calculate the frequency of the allele. Based on the Punnett square breakdown of Hardy-Weinberg (fig 22-3 & 22-4), we can see that f(aa) = q^2. So first, calculate the frequency of homozygous recessive (affected) individuals: f(aa) = 1/3600 So then, take the square root of f(aa) to get q: Once you have q, you can solve for p by using p + q = 1: Now that we have a value for q, we can again use the Punnett square breakdown to solve for f(Aa). f(Aa) = 2pq
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