| XH | Y | |
|---|---|---|
| XH | XHH Unaffected female | XHY Unaffected male |
| Xh | XhH Carrier female | XhY Affected male (Haemophilia) |
Predicted offspring ratios
- Unaffected females: 1/4 (25%)
- Carrier females: 1/4 (25%)
- Affected females: 0/4 (0%)
- Unaffected males: 1/4 (25%)
- Affected males: 1/4 (25%)
Capital letter = dominant allele on the X chromosome. Lower case = recessive. The Y chromosome carries no allele for this gene, so a single recessive allele expresses the trait in males.