Question

consider a sex - linked inherited disease like hemophilia. males are never hidden carriers of this type of inherited disease. why?
a males only inherit the gene for the disease from their mothers.
b males cannot inherit the normal disease - free gene from either parent.
c males do not have a second x chromosome that could mask the gene for hemophilia.
d the y chromosome found in males is a recessive chromosome and cannot carry the dominant gene for hemophilia.

Explanation:

• Option A: While males inherit the X - linked gene from their mothers, this does not explain why they are not carriers.
• Option B: Males can inherit a normal X - chromosome from their mothers (if the mother is not a carrier or is a carrier with a 50% chance of passing the normal X).
• Option C: Males have one X and one Y chromosome (\(XY\)). For X - linked recessive diseases like hemophilia, if a male inherits the recessive allele on the X - chromosome, there is no second X - chromosome (as in females \(XX\)) to provide a dominant, non - disease allele to mask the recessive disease allele. So, they either express the disease (if they get the recessive X) or are unaffected (if they get the normal X), and cannot be carriers.
• Option D: The Y chromosome does not carry the gene for hemophilia (which is on the X - chromosome), and the concept of the Y chromosome being recessive in this context is incorrect.

Answer:

C. Males do not have a second X chromosome that could mask the gene for hemophilia.