A man with free earlobes and the ability to taste PTC marries a woman with free earlobes and no ability to taste PTC. They have four children. All of the children are tasters of PTC. Only one has attached earlobes. What are the genotypes of the parents?

Father's genotype is T T, E e

Mother's genotype is t t, E e

Explanation:

Tasting PTC

Let the characters for tasting and not tasting PTC be T and t respectively.

Since all the children can taste PTC, it can be deduced that tasting PTC is a dominant trait.

The man will be homo-zygous dominant for tasting PTC while the woman is homo-zygous recessive for tasting PTC.

Genotype of man is T T and genotype of woman is t t

T T x t t = T t,  , T t, T t; which is a 4:0 phenotype.

Earlobes:

Let the characters for Free and attached earlobes be E and e

Since both the man and woman have free earlobes and 3 out of 4 children have free earlobes, it can be deduced that free earlobes is dominant while attached earlobes is recessive.

The ratio of free to attached earlobes is 3:1

The man and the woman are both hetero-zygous dominant, E e for free earlobes, so that a cross between them will yield three hetero-zygous dominant for free earlobes and one homo-zygous recessive for attached earlobes.

E e x E e = E E, E e, E e, e e; which is a 3 : 1 phenotype.

b is the correct answer