Question

Phenylthiocarbamide (PTC) is an organic compound that either tastes extremely bitter or is tasteless, depending on the genotype of the taster. The tasting allele is dominant over the non-tasting allele. Normal skin pigmentation is dominant over albinism. (it is important to note that this example of PTC tasting cannot be explained with simple genetics, but for the purpose of this question, assume that it can) A normally-pigmented woman who cannot taste PTC has an albino father who can taste PTC. The woman married an albino man who can taste PTC and whose mother cannot taste PTC. For the married couple, 1. correctly identify their genotypes, (1 mark) 2. complete a Punnett square showing the expected offspring of the couple, and (1 mark) 3. identify the genotypic and phenotypic ratios of their offspring (1 mark) i. B I I U Ꭶ X2 x? I ** С 0

Answer 1

Dominant allele = P = Tasters
Recessive allele = p = Non-tasters

Dominant allele = A= Normal skin
Recessive allele = a = Albino

Man = aaPp
His mother = Aapp
Woman = Aapp
Her father = aaPp

Parental cross: Aapp X aaPp
Progeny:
Ap/aP = Normal skin and taster
ap/aP = Albino and taster
Ap/ap = Normal skin and non-taster
ap/ap = Albino and non-taster

Genotypic ratio = 1:1:1:1
Phenotypic ratio = 1:1:1:1