#16 Some people can taste the bitter compound phenyl-thiocarbamide while others
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Question
#16 Some people can taste the bitter compound phenyl-thiocarbamide while others cannot. This trait is governed by a single autosomal gene; the allele for tasting is completely dominant with respect to the allele for nontasting. Among 1707 Hawaiians tested for the ability to taste, 1326 tasters were found. Assume that the population is at Hardy-Weinberg equilibrium for this gene and that mating is purely random: a. What are the allele frequencies for the tasting allele Y[= (p)] and for the nontasting allele t [= (q)]? b. What are the genotype frequencies in the population? c. Of all the matings in the population, what proportion will be between two nontasters? d. Of all the matings in the population, what proportion will he between a taster and a nontaster? e. Of all the matings in the population, what proportion will he between a taster male and a nontaster female? f. What proportion of all of the progeny produced by all matings between a taster male and a nontaster female will be nontasters? g. Of all the matings in the population, what proportion will be between two tasters?Explanation / Answer
Phenylthiocarbamide or PTC is bitter to taste and only few individuals can experience the taste but the others cannot. The PTC is controlled by a dominant allele T; individuals possessing the 'T' can taste the compound. The individuals with homozygous recessive allele 't' cannot taste the PTC compound. Then, the frequencies are as follows.
Frequency of T (allele p) in the given population = 1326/1707 = 0.78 = 78%
Frequency of t (allele q) in the population = 381/1707=0.22=22%
Estimated frequency of t = q = q2 = 0.22 = 0.47
Estimated frequency of T= p = 1 – q = 1 – 0.47 = 0.53
Frequency of the genotype TT = p2 = (0.53)2 = 0.2809
Frequency of genotype Tt = 2pq = 2 (0.47) (0.53) = 0.4982
Frequency of the genotype tt = q2 = (0.47)2 = 0.2209
Of the population, the tasters would be 53% and nontasters would be 47%.
Of all of the progeny produced by all matings between taster male (TT) and nontaster female (tt), the nontaster progeny (tt) would be 25% because the offspring produced will be in 3:1 proportion.
Of all the matings in the population, the proportion of two tasters will be 50% (25% -TT; 25% - Tt).
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