Q.Explain the inheritance of sex linked characters in human being.

Step 1. Recall the two categories: sex-linked genes sit in the differential (non-homologous) regions of the X or Y chromosome, and since these regions cannot cross over, X-linked and Y-linked genes are inherited quite differently from each other.

Step 2. Explain X-linked inheritance using haemophilia and colour blindness: both are recessive X-linked conditions. Because males are hemizygous for X-linked genes (a single X, no masking second copy), they express the recessive trait from just one copy, while females need it on both X chromosomes — this is why these conditions are far commoner in men. Tracing a cross between a colour-blind man and a normal woman shows the criss-cross pattern: the F1 generation has all sons normal and all daughters unaffected carriers, and colour blindness resurfaces only in the carrier daughter's own sons in the next generation. …

Cover both X-linked (haemophilia/colour blindness, criss-cross pattern) and Y-linked (hypertrichosis, holandric) inheritanc …

• Answering only about X-linked inheritance and omitting Y-linked (holandric) inheritance, when the questi …