In humans, the presence of chin and cheek dimples is dominant to the absence of
ID: 49478 • Letter: I
Question
In humans, the presence of chin and cheek dimples is dominant to the absence of dimples, and the ability to taste the bitter compound PTC (phenylthiocarbamide) is dominant to the inability to taste this compound. Both traits are under the control of autosomal genes that are unlinked.
A population from Ghana is examined, and the following allele frequencies are calculated.
Dimples
Frequency
Tasting
Frequency
D
0.62
T
0.76
d
0.38
t
0.24
a. Determine the frequency of genotypes for each gene. with work shown
b. What are the expected frequencies of the four possible phenotype combinations:
dimpled tasters, undimpled tasters, dimpled nontasters, and undimpled nontasters? with work shown
Dimples
Frequency
Tasting
Frequency
D
0.62
T
0.76
d
0.38
t
0.24
Explanation / Answer
Hardy and Weinberg is, p2 + 2pq + q2 = 1.
Where, p2 = homozygous dominant individuals
2pq = heterozygotes
q2 = homozygous recessive individuals
a.) The frequency of different genotypes can be calculated as follows.
The frequency of individuals with homozygous dominant allele(DD) = (0.62)(0.62) = 0.3844
The frequency of individuals with heterozygous allele (Dd) = 2pq = (2)(0.62)(0.38) = 0.4712
The frequency of individuals with homozygous recessive allele (dd) = (0.38)(0.38) = 0.1444.
Frequency of taste genes:
The frequency of individuals with homozygous dominant allele (TT) = (0.76)(0.76) = 0.5776
The frequency of individuals with heterozygous allele (Tt) =2pq = (2)(0.76)(0.24) = 0.3648
The frequency of individuals with homozygous recessive (tt) = (0.24)(0.24) = 0.0576.
b.) The frequency of individual with dimples (Homozygous dominent + heterozygous) = 0.3844+0.4712 = 0.8556
The frequency of individual without dimples (homozygous recessive) = 0.1444
The frequency of individual with taste for PTC (Homozygous dominent + heterozygous) = 0.5776+ 0.1824 = 0.944
The frequency of individual without taste for PTC (homozygous recessive) = 0.0576