Essential Genetics 6th Edition by Daniel Hartl

Exercise 6

The most common form of color blindness in humans results from X-linked recessive alleles. One type of allele, call it cb r, results in defective red perception, whereas another type of allele, call it cbg, results in defective green perception. A woman who is heterozygous cbr/cbg and a normal male produce a son whose chromosome constitution is XXY. What are the possible genotypes of this child under each of the following circumstances?
(a) The nondisjunction took place in meiosis I in the mother.
(b) The nondisjunction took place in the cbr-bearing chromosome in meiosis II in the mother.
(c) The nondisjunction took place in the cbg-bearing chromosome in meiosis II in the mother.