Question

question 14 1 pts hemophilia is a sex - linked recessive disease. a phenotypically normal woman has phenotypically normal parents. however, she has a hemophiliac brother. what are her parents genotypes?
options:
xhxh & xhy
xhxh & xhy
xhxh & xhy
xhxh & xhy
xhxh x xhy

(another question: hemophilia is a sex - linked recessive disorder. a phenotypically normal man marries a homozygous normal woman. what is the probability that any of their children will be hemophiliacs?
options:
0%
25%
50%
75%
100%)

Explanation:

First Sub - Question (Probability of children being hemophiliacs)

Step1: Determine parental genotypes

The man is phenotypically normal and since hemophilia is X - linked recessive, his genotype is $X^HY$ (because males have one X and one Y, and a normal male can't have the recessive allele for hemophilia on his X as that would make him hemophilic). The woman is homozygous normal, so her genotype is $X^HX^H$.

Step2: Analyze possible offspring genotypes

When we do a cross between $X^HX^H$ (mother) and $X^HY$ (father), the possible gametes from the mother are all $X^H$, and from the father are $X^H$ and $Y$.

• For daughters: They will get one $X^H$ from mother and one $X^H$ from father, so genotype $X^HX^H$ (normal).
• For sons: They will get one $X^H$ from mother and one $Y$ from father, so genotype $X^HY$ (normal).

Since all possible offspring genotypes result in a normal phenotype (no hemophilia), the probability that any of their children will be hemophiliacs is 0%.

Step1: Recall hemophilia inheritance

Hemophilia is X - linked recessive. A hemophilic male has genotype $X^hY$ (since he has the recessive allele on his X chromosome and Y has no corresponding allele).

Step2: Analyze parental phenotypes and genotypes

The woman's parents are phenotypically normal. For a son to be hemophilic ($X^hY$), he must have received the $X^h$ allele from his mother (since he gets Y from father). So the mother must be a carrier (heterozygous) because she is phenotypically normal. A phenotypically normal mother with a hemophilic son has genotype $X^HX^h$. The father is phenotypically normal, so his genotype is $X^HY$ (since he has a normal phenotype and is male, so his X is normal).

So the parents' genotypes are $X^HX^h$ (mother) and $X^HY$ (father), which corresponds to the option $X^HX^h$ & $X^HY$.

Answer:

0%

Second Sub - Question (Parental genotypes of the woman with a hemophilic brother)