3 The ability to taste phenylthiocarbamide PTC in humans app

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?

Solution

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).