3. The ability to taste phenylthiocarbamide (PTC) in humans appears to be due to

Question

3. The ability to taste phenylthiocarbamide (PTC) in humans appears to be due to a dominant factor. These persons are called tasters. A man who is a taster, and who has a non-taster mother, marries a woman who is a taster. She has 3 brothers and 2 sisters, three of whom are non-tasters. What chances will the children of this marriage have of being non-tasters?

4. Twenty-five percent of the offspring of a certain pair of white sheep are black. What was the genotype of the parents?

5. A woman has a rare abnormality of the eyelids called ptosis, which makes it impossible for her to open her eyes completely. The condition is due to a dominant gene (P). The woman's father had ptosis, but her mother had normal eyelids. What are the genotypes of the woman, her father, and her mother? If she married a man with normal eyelids, what proportion of the children would be expected to have ptosis and what proportion would be normal?

Explanation / Answer

3. Both parents are carriers of the dominant trait (taster). Their children will inherit as follows

Of the daughters 100% will have the disorder since all of the daughter will receive a copy of their father's X chromosome.

Of the sons, 50% will have disorder, 50% will be completely unaffected. Sons have an equal chance of receiving either of their mother's X chromosome.

4. White is dominant = W

Black is recessive = w

Parents= homozygous white (WW) + heterozygous white (Ww). Or

Parents = heterozygous white (Ww) + heterozygous white (Ww).

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