Question

1) imagine a sex-linked dominant disease found on the x-chromosome of humans. if the offspring of a certain mating pair have a 50% chance of receiving the disease, regardless of gender, which of the following statement is true? explain your choice

The father has the disease

The mother is heterozygous for the disease

The mother is homozygous for the disease

The mother does not have the diseae

2) a young girl is diagnosed with duchenne muscular dystrophy ( x linked recessive) and her mother is pregnant with baby boy. which of the following must be true? explain your choice

Her Father's Father had the disease

Her brother will have the disease

Her father had the disease

Her mother had the disease

Her father's mother was a carrier

Answer 1

1. Option B is correct.
XD = Mutant dominant allele
Xd = WT recessive allele
Parental cross: XDXd X XdY
Progeny: XDXd XDY XdXd XdY
Here, half the males and half the females are affected. As a whole, half the progeny are affected irrespective of their gender.

2. Option C is correct.
Xm = Mutant recessive allele
XM = WT dominant allele
Parental cross: XMXm X XmY
Progeny: XmXm XmY XMXm XMY

Affected daughter = XmXm
She can be affected only when her father is also affected (He must contain the disease-causing allele).