Male sex is determined byb Y- cyhromosome which doe not bear the gene for haemophilia. In the given case, when a normal male marries a carrier female the resultant offsprings wil be as follows -
This marriage results in the four type sof offsprings in equal ratio, i.e.,
Normal Girt with XX genotype Normal boy with XX genotype Carrier Girl with `XX^(h)` genotype Haemophilia boy with `X^(h)Y` genotype The defect of haemophilia does not appear in the girl carrier because the second X- chromosome possesses the allel for normal blood clotting. 50% of boys develop haemophilia because Y chromosomes does not carry allele for blood clotting. Therefore, female child can be a carrier but does not develop disease. The male child, on the other hand, can develop the disease.
