Xg is an antigen found on red blood cells This antigen is ca

Xg is an antigen found on red blood cells. This antigen is caused by an X-linked allele (Xa) that is dominant over an allele for the absence of the antigen (X-). The inheritance of these X-linked alleles was studied in children with chromosome abnormalities to determine where nondisjunction of the sex chromosomes occurred. For which mating below, did nondisjunction take place in the mother?

XaY × X-X- Xa (Turner syndrome)

XaY × XaX- X- (Turner syndrome

)XaY × X-X- XaX-Y (Klinefelter syndrome)

XaY × XaX- X-X-Y (Klinefelter syndrome)

Nondisjunction occurred in the mother for choices A and D.

Solution

XaY × X-X- Xa (Turner syndrome)
&

XaY × XaX- X-X-Y (Klinefelter syndrome).

In both these cases, non disjunction took place in maternal parent.