QUESTION 9 if a woman who is a carrier for Fragilex syndrome (an X-linked disorder) has children with a man who does not have the disorder, what chance do their
daughters have of being carriers of Fraglese
None
50%
25%
100%

Daughters who are descendants of a woman carrier of Fragile X Syndrome and a healthy man will have a 50% chance of having or being carriers of the syndrome.

Explanation:

Fragile X syndrome has an autosomal dominant inheritance pattern, linked to the X chromosome. That is, someone with an altered X chromosome can either be a carrier or have the syndrome.

In this case, the mother is a carrier of the altered chromosome (X) while the father is neither a carrier nor has the condition (XY).

Cross X x XY

Alleles         X           Y

           X       Y

X               XX          XY

The couple has a 50% chance of having daughters, and of those daughters half (50%) have the chance of having an Xf chromosome, and being a carrier or suffering from the syndrome.