Question

which of the following is the genotype of the circled individual in generation ii?
genotype key:
$x^h$= normal $f8$ allele
$x^h$= mutant $f8$ allele
choose 1 answer:
a $x^hy$
b $x^hx^h$
c $x^hx^h$
d $x^hx^h$

Explanation:

1. First, analyze the pedigree: The circled individual in generation II is a female (circle symbol) and has a son with the mutant trait (black square, indicating X - linked recessive inheritance, likely hemophilia as F8 is related to factor VIII, involved in hemophilia A).
2. In X - linked recessive inheritance, a carrier female (who does not show the trait but can pass it on) has one normal allele ($X^{H}$) and one mutant allele ($X^{h}$).
3. The circled female has a affected son (genotype $X^{h}Y$), so she must have passed the $X^{h}$ allele to her son. Since she is not affected (her symbol is a white circle, not black), she must have a normal allele $X^{H}$ as well. So her genotype should be $X^{H}X^{h}$.

• Option A ($X^{H}Y$) is a male's genotype, so it's incorrect.
• Option B ($X^{H}X^{H}$) would mean she can't pass on the mutant allele, but she has an affected son, so incorrect.
• Option C ($X^{h}X^{h}$) would mean she is affected (black symbol), but she is white, so incorrect.
• Option D ($X^{H}X^{h}$) fits the carrier status as she has a normal and a mutant allele, can pass the mutant allele to her son, and is not affected herself.

Answer:

D. $X^{H}X^{h}$