Question

What will be the phenotype of the progeny, if a carrier haemophilic female marries a normal male? Explain.

Answer 1

The genotype of the carrier female is $X^H{X}^h$. The genotype of the male with normal blood clotting is $X^{H}Y$.

If a carrier female $\left(X^H{X}^h\right)$ marries a male having normal blood clotting factor $\left(X^{H}Y\right)$, then the daughters will have genotype $X^H{X}^H$ (normal) and $X^H{X}^h$ (carrier). All the daughters will have normal clotting of blood but half of them will be carriers. The genotype of the sons will be $X^{H}Y$ (normal) and $X^{h}Y$ (haemophilic). Half the sons will be haemophilic while remaining will have normal clotting of blood. From the above cross, it is evident that the pattern of inheritance of haemophilic is criss-cross as the gene of the disorder is transmitted from grandfather to grandson through his daughter.