Question

Recently a girl baby has been reported to suffer from haemophilia. How is it possible? Explain with the help of cross.

Answer 1

For the girl child to have haemophilia both the father and mother should have haemophilia or the mother should atleast be a carrier of the disease. Since, haemophilia is an X-linked recessive disorder, so both the X chromosomes in the girl child must be diseased for the girl child to have the disease. If the mother is a carrier and the father diseased then, the child needs to receive the diseased X- chromosome from the mother for her to have the disease and therefore there is 50% certainty of having the disease.. If however, the mother and father both are diseased the girl child will definitely have the disease as she will get a diseased X-chromosome from both the parent.