Question

you meet a young male with hemophilia, an x - linked recessive disorder. while talking to him, he mentions that his maternal grandfather also had hemophilia, but his parents do not. which of the following statements about his family would be correct?
correct answer(s)
he could pass the gene for hemophilia on to his future daughters.
his sister would also be a hemophiliac.
his maternal grandmother also had hemophilia.
his father is a genetic carrier of hemophilia.
he could pass the gene for hemophilia on to his future sons.
his mother is a genetic carrier for hemophilia.
incorrect answer(s)

Explanation:

• He could pass the gene for hemophilia on to his future daughters: Males have an X and a Y chromosome. Since hemophilia is X - linked recessive, he has the hemophilia gene on his X chromosome. Daughters inherit one X chromosome from their father. So, he can pass the X - linked hemophilia gene to his daughters.
• His mother is a genetic carrier for hemophilia: His maternal grandfather had hemophilia (X⁻Y, where X⁻ is the hemophilia - carrying X chromosome). His mother inherited one X from her father (the X⁻) and one from her mother. Since his parents do not have hemophilia (father is XY, mother is a carrier X⁻X), she must be a carrier.

• His father is a genetic carrier of hemophilia: Males have XY chromosomes. If a male had the hemophilia gene (X⁻Y), he would have hemophilia. Since his father does not have hemophilia, his father cannot be a carrier (carriers are typically females with one normal and one affected X chromosome in X - linked recessive disorders).
• He could pass the gene for hemophilia on to his future sons: Sons inherit the Y chromosome from their father. Since the hemophilia gene is on the X chromosome, he cannot pass the hemophilia gene to his sons through his Y - chromosome.
• His sister would also be a hemophiliac: For a female to be hemophiliac (X⁻X⁻), she needs to inherit an X⁻ from both parents. We know the father is XY (no X⁻) and the mother is a carrier (X⁻X). So, the sister has a 50% chance of being a carrier (X⁻X) and 0% chance of being hemophiliac (assuming the father is normal XY)
• His maternal grandmother also had hemophilia: We only know the maternal grandfather had hemophilia. The maternal grandmother could be normal (XX) or a carrier (X⁻X). There is no information to suggest she had hemophilia (X⁻X⁻)

Answer:

Correct Answer(s):

• He could pass the gene for hemophilia on to his future daughters.
• His mother is a genetic carrier for hemophilia.

Incorrect Answer(s):

• His father is a genetic carrier of hemophilia.
• He could pass the gene for hemophilia on to his future sons.
• His sister would also be a hemophiliac.
• His maternal grandmother also had hemophilia.