Who has the xy chromisine?

Males have the XY Chromosome.

Females have the XX Chromosome. Labelled x'x" for the exervise.

When combining and to make sure the genders remain at 50% M & 50% F .

Hence

X'Y = M

X"Y = M

XX' = F

XX" = F

So you can see from the four possible outcomes , two are male and two are femeale, maintaining 50% of each gender in the population.