Dec 14, 2013
somewhere in the northeast baby
MD/PhD Student
Here is a verbatim restatement of the question (page 196 edition 7th biology orsay) Question 44
44. A color blind man marries a healthy woman. They have two children both with turner's syndrom, one of the children is color blind. which is true

A. Nondisjunction occurred in father for both
C non disjunction occured in mother for color blind child and in father for child with normal vision

The answer key says C, which could be true. However, A can also be true? Since mother can also be a carrier, so we can have both cases of turner syndrome where the mutant X and wildtype X from mother passed onto the offspring with only one X chromosome; am I reasoning correctly? I just took genetics so this looks a bit trivial but i was surprised byt he answer in the book


rye sense of humor
5+ Year Member
Feb 26, 2012
Medical Student
Yes your reasoning is correct, but when they say the woman is healthy, they mean she has two normal X chromosomes (genotype healthy, as well as phenotype healthy).

Genetics questions are annoyingly ambiguous sometimes. I've found it works best to assume people are 100% healthy unless proven otherwise.