Question

6. About 70% of Americans get a bitter taste from the substance called phenylthiocarbamide (PTC). It is tasteless to the rest. The "taster" allele is dominant to non-taster. Also, normal skin pigmentation is dominant to albino. A normally pigmented woman who is taste-blind for PTC has an albino-taster father. She marries an albino man who is a taster, though the man's mother is a non-taster. 1 pt

            A. What are the genotypes of the woman and man?

            B. What phenotypes and in what proportion would you expect in their children?

Answer 1

A) let the taster allele be represented as "TT" and the non-taster allele be represented as "tt".

similarly the normal pigmentation represented as "AA" and the albino as "aa".

according to question, the normally pigmented woman who is taste blind can have only two possible genotypes as - "AAtt" or "Aatt" but this is also given in the question that her father was albino-taster, therefore the possible genotype of his father would be "aaTt" or "aaTT".

crossing between all the possible genotypes of the woman's mother with her father concluded that her genotype will be "Aatt" only because his father is an albino.

similarly for the man - who is albino and taster, his possible genotypes will be either "aaTt" or "aaTT".

since we know his mother is a non-taster, therefore, the only possible genotype of the man would be "aaTt".

B) the cross between "Aatt" and "aaTt" will result in

AaTt Aatt aaTt aatt

therefore the phenotypic ratio will be

pigmented taster : pigmented non-taster : albino taster : albino non-taster

1 : 1 : 1 : 1