A man and a woman are both carriers for two autosomal recessive disorders, PKU (chromosome 12) and cystic fibrosis (chromosome 7). If they have a daughter, what is the probability that she will have PKU but not CF?

Pr = (3/16)

Explanation:

It was stated that both the man and the woman are both carriers for two autosomal recessive disorders, PKU (chromosome 12) and cystic fibrosis (chromosome 7).

∴ let Aa¹Bb° represent the traits in the Man

Where;

Aa¹ = carrier of PKU

Bb° = carrier of cystic fibrosis

Also, let Cc¹Dd° represent the traits in the woman

Where;

Cc¹ = carrier of PKU

Dd° = carrier of cystic fibrosis

Now, if Aa¹Bb° self-crossed, we'll have the F1 progeny as AB, Ab°, a¹B and a¹b°

also, if Cc¹Dd° self-crossed, we have CD, Cd°, c¹D and c¹d° as their F1 progeny

In the F2 generation, the dihybrid cross between the F1 generations will be:

AB, Ab°, a¹B, a¹b° * CD, Cd°, c¹D, c¹d°

ACBD, ACb°D, a¹CBD, a¹Cb°D

ACBd°, ACb°d°, a¹CBd°, a¹Cb°d°

Ac¹BD, Ac¹b°D, a¹c¹BD, a¹c¹b°D

Ac¹Bd°, Ac¹b°d°, a¹c¹Bd°, a¹c¹b°d°

Only (a¹CBD, Ac¹BD, a¹c¹BD) shows the probability that she will have PKU but not CF.