In humans, the presence of chin and cheek dimples is dominant to the absence of
ID: 49439 • 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. a. Determine the frequency of genotypes for each gene. b. What are the expected frequencies of the four possible phenotype combinations: Dimpled tasters, undimpled tasters, dimpled nontasters, and undimpled nontasters?Explanation / Answer
Part a-
For dimples:
DD = p2 = 0.62*0.62 = 0.3844
Dd = 2pq = 2 * 0.62 * 0.38 = 0.0471
dd = q2 = 1 - [p2 + 2pq] = 0.1444
For PTC tasting:
TT = p2 = 0.76 * 0.76 = 0.5776
Tt = 2pq = 2 * 0.76 * 0.24 = 0.3648
tt = q2 = 1 - [0.5776+0.3648] = 0.0576
Part b-
To find the combination of frequencies, we will use the rules of probability.
Dimpled tasters: [DD+Dd] * [TT+Tt] = [0.3844+0.0471] * [0.5776+0.3648] = 0.4315 * 0.9424 = 0.4066
Undimpled tasters: [dd] * [TT+Tt] = 0.1444 * 0.9424 = 0.136
Dimpled nontasters: [DD+Dd] * [tt] = 0.4315 * 0.0576 = 0.0248
Undimpled nontasters: [dd] * [tt] = 0.1444 * 0.0576 = 0.0083