The ability to taste the chemical phenylthiocarbamide is an autosomal dominant phenotype, and the inability to taste it is recessive. If a taster woman with a nontaster father marries a taster man who in a previous marriage had a nontaster daughter, what is the probability that their first child will be:

a. a nontaster girl?

b. a taster girl?

c. a taster boy

a. a nontaster girl = 1/8

b. a taster girl = 3/8

c. a taster boy = 3/8

Explanation:

Let's assume that the allele "T" is responsible for the taster phenotype while the recessive allele "t" gives the nontaster phenotype. The taster woman had a nontaster father (tt). Therefore, she is heterozygous dominant (Tt). The taster man had a nontaster daughter (tt) which means that he also has one "t" allele and his genotype is "Tt".

A cross between Tt and Tt would produce progeny in following ratio=

Tt x Tt = 3/4 taster: 1/4 nontaster

The probability of sons and daughters during each reproduction is=

XX x XY = 1/2 XX and 1/2 XY

Therefore,

a. probability of having a nontaster girl = 1/4 x 1/2 = 1/8

b. a taster girl = 3/4 x 1/2 = 3/8

c. a taster boy = 3/4 x 1/2 = 3/8