In humans the presence of chin and cheek dimples is dominant to the absence of dimples, and the ability to taste the compound PTC is dominant to the inability to taste the compound. Both traits are autosomal and they are unlinked.

The frequencies of alleles for dimples are; D=0.62 and d=0.38.

The frequencies of alleles for tasting are; T=0.76 and t=0.24.

What is the expected frequencies for undimpled tasters?

Question

Fleming

Biology

22 August, 08:57

In humans the presence of chin and cheek dimples is dominant to the absence of dimples, and the ability to taste the compound PTC is dominant to the inability to taste the compound. Both traits are autosomal and they are unlinked.

The frequencies of alleles for dimples are; D=0.62 and d=0.38.

The frequencies of alleles for tasting are; T=0.76 and t=0.24.

What is the expected frequencies for undimpled tasters?

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Answers (1)

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Bobby Hogan · Answer 1

The frequency of undimpled tasters is 0.136.

Explanation:

The Hardy-Weinberg law illustrated all the probable genotypes for a gene with two alleles. The binomial expansion signifying this is, p2+2pq+q2 = 1.0

Here, p2 is the proportion of homozygous dominant individuals, q2 refers to the proportion of homozygous recessive individuals, and 2pq is the proportion of heterozygotes.

Thus, on the basis of the given data, the frequencies for dimples phenotypes are:

The frequency of homozygous dominant allele carrying individuals (DD) = 0.62 * 0.62 = 0.3844

The frequency of heterozygous allele carrying individuals (Dd) = 2 * 0.62 * 0.38 = 0.4712

The frequency of homozygous recessive allele carrying individuals (dd) = 0.38 * 0.38 = 0.1444

Thus, from the above frequencies, the frequency of individuals with dimples (DD and Dd) = 0.3844 + 0.4712 = 0.8556

The frequency of individuals without dimples (dd) = 0.1444.

The frequencies for tasting phenotypes:

The frequency of homozygous dominant allele carrying individuals (TT) = 0.76 * 0.76 = 0.5776

The frequency of heterozygous allele carrying individuals (Tt) = 2 * 0.76 * 0.24 = 0.3648

The frequency of homozygous recessive allele carrying individuals (tt) = 0.24 * 0.24 = 0.0576

Thus, from the above frequencies:

The frequency of individuals with taste for PTC (TT and Tt) = 0.5776 + 0.1824 = 0.944

The frequency of individual without taste for PTC (tt) = 0.0576

As it is a dominant mode of inheritance the genotype of undimpled tasters is either ddTt or ddTT.

The frequency of taster individuals will be TT + Tt = 0.5776 + 0.3648 = 0.9424

Now, the expected frequency of undimpled tasters will be the product of frequency of dimpled and frequency of tasters = 0.144 * 0.9424 = 0.1357.

Therefore, the frequency of the undimpled tasters is 0.136.