D3.2.12—Haemophilia

hemophilia is due to a recessive allele/is a recessive trait/ $\mathrm{X}^{\mathrm{H}}$ is normal allele and $\mathrm{X}^{\mathrm{h}}$ is hemophilia allele;
hemophilia is sex linked;
allele/gene is on the X chromosome;

Marking guidance:

Reject disease/hemophilia carried on X chromosome.
(sex chromosomes in) females are XX while males are XY;
Y chromosomes do not have the allele/hemophiliac males are $\mathrm{X}^{\mathrm{h}} \mathrm{Y}$;
males inherit their X chromosome from their mother/do not pass the allele to sons;
males have only one copy so recessive trait/allele is not masked;
males have a 50 % chance of hemophilia/receiving the allele if mother is a carrier;
carrier is heterozygous for the gene/is $\mathrm{X}^{\mathrm{H}} \mathrm{X}^{\mathrm{h}}$;
dominant/normal allele masks the recessive allele (so clotting is normal);
females inherit one X chromosome from father and one from mother;
affected/hemophiliac males have carrier daughters;
hemophilia allele could have been inherited from either parent;

Accept the points above explained either in text or clearly using a Punnett grid or genetic diagram, but not for simply reproducing an unlabeled Punnett grid or diagram without explanation.