Question

6. In class we discussed autosomal polymorphisms such as widow’s peak and detached

ear lobes, both of which are dominant traits. Suppose that a man with a widow’s peak and

attached ear lobes (whose father had detached ear lobes) marries a woman without a widow’s

peak and detached ear lobes (whose father had attached ear lobes). What is the probability

that their first child will:

a.not have a widow’s peak or attached ear lobes?

b.have both a widow’s peak and detached ear lobes?

c.have a widow’s peak and attached ear lobes?

Answer 1

It is given here that the father of the man had detached ear lobes but genotype of mother is not given. Hence, there are two scenarios for genotype of the man and it can be assumed as either Wwdd or WWdd. The genotype of woman he marries will be wwDd. We will now make a punnett square for each scenario and answer:

Scenario 1: Wwdd X wwDd

	Wd	wd
wD	WwDd	wwDd
wd	Wwdd	wwdd

From the punnett square the aswers are:

a. The genotype for not widow's peak or attached lobes will be wwdd. Thus, the probability of 1st child with these traits is 1/4.

b. The genotype for widow's peak as well as detached lobes will be WwDd. Thus, the probability of 1st child with these traits is 1/4.

c. The genotype for widow's peak and attached lobes will be Wwdd. Thus, the probability of 1st child with these traits is 1/4.

Scenario 2: WWdd X wwDd

	Wd
wD	WwDd
wd	Wwdd

From the punnett square the aswers are:

a. The genotype for not widow's peak or attached lobes will be wwdd. Thus, the probability of 1st child with these traits is 0.

b. The genotype for widow's peak as well as detached lobes will be WwDd. Thus, the probability of 1st child with these traits is 1/2.

c. The genotype for widow's peak and attached lobes will be Wwdd. Thus, the probability of 1st child with these traits is 1/2.