1. Cystic fibrosis (CF) is a life threatening genetic disease affecting most cri
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Question
1. Cystic fibrosis (CF) is a life threatening genetic disease affecting most critically the lungs, and also the pancreas, liver, and intestine. It is characterized by abnormal transport of chloride and sodium ions across the epithelium, leading to thick, viscous secretions in the airways. CF results from the homozygous recessive condition, afflicting one out of every 2,500 babies in the Caucasian population
a) Bepari, Paul, Malakar, and Chakraborty analyzed 29 countries for the prevalence of the cystic fibrosis allele For each of the following countries, calculate the probability of a child being born with cystic fibrosis:
i. Switzerland has the highest gene frequency ( 0.022 gene frequency for the CF allele)
ii. Japan has the lowest gene frequency (0.002 gene frequency for CF)
b) In comparison to Caucasians, the frequency of CF heterozygous carriers is lower for minority groups, including Hispanics (1 in 46), African Americans (1 in 60) and Asians (1 in 150). Experiments have shown that CF carriers have saltier sweat than people with two normal alleles. From an evolutionary standpoint, speculate why the salty sweat characteristic may explain the differences in CF heterozygous frequencies among different minority groups in the U.S.
c) CSC enrolls approximately 3,000 students, of which 6.4% are Hispanic/Latino, 3.9% are Black or African American, and 0.5% are Asian. (Another 10.5% are unspecified or two or more races, 2.2% are non-resident aliens, 1.3% are American Indian or Alaska native. As we cannot speculate on the allele frequency of these groups, assume that their CF allele frequency mirrors that of the general U.S. Caucasian population.) Assuming that the CSC population reflects this general frequency of the CF allele frequency, approximately how many CSC students may have the heterozygous phenotype (i.e., would be carriers)?
Explanation / Answer
The frequency can be calculated through Hardy - Weinberg equation . Since only homozygous recessive are afflicted , the frequency would be (22×10^-3 )^2 = 22×22× 10^-6 =484 Per
Million .
ii) using same formula , the prevalence in Japan would be 484 per hundred million , as frequency of allele is 10 times lower , the prevalence would be 10^2 times Lesser .
) The answer to third subpart may be - that those living in hotter and more humid conditions , could not afford to loose excessive salts/ electrolytes , hence natural selection would tend to favor the individuals with Both Normal alleles , over CF heterozygous , thereby reducing the frequency of CF allele in those populations .
iv )Since , at the start of question , we were provided with the prevalence in Caucasian population , and since this subpart asks to assume the frequency in the given sample to be similar as in Caucasians , the first step is to calculate the frequency in Caucasian population .
Using the Hardy - Weinberg equation - the frequency would be , since q^2 =1/2500 , hence q =1/50 = 0.02 . Now we have to calculate the fraction of heterozygous . Since q= 0.02 , P = 1-0.02 = 0.98 . Now , heterozygous are equal to 2pq = 2×0.02 ×0.98 =196×10^ -4 . Now Number of heterozygous in given population is 196×3×10^3×10^ -4 = 588 ×10^ -1 =58.8 , i.e. 59 are likely to be heterozygous for the CF Allele in given population .
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