Question

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

Answer 1

Answer:

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