In a genetic cross, if a male has XY sex chromosomes and a female has XX sex chromosomes, what is the probability of having a male offspring?

Misinterpreting Ratios in Sex‑Determination Crosses

Students often treat the 1:1 ratio of male to female offspring as a fixed rule, ignoring that the ratio depends on the sex of the parent and the specific cross (e.g., XX × XY vs. XY × XY).

Explain that the 1:1 ratio applies only when one parent contributes a single sex chromosome (XX or XY) and the other contributes a single sex chromosome (XY). Use a simple Punnett square to show how the ratio changes when both parents are XY (giving 1/4 XX, 1/2 XY, 1/4 YY) or when both are XX (all XX). Emphasise that the ratio is derived from the proportion of gametes, not a universal rule.