ICSE - X - Biology - Genetics - Some Basic Fundamentals
pls ans the 66th question:
X - normal X chromosome
Y - normal Y chromosome
Xh - X chromosome with hemophilia linked gene
Father = XhY (if the man has hemophilia, he must be carrying an Xh)
Mother =XhX (Since fathers only have one X gene to pass on to their daughters, this affected father obviously only had an Xh gene to pass down to his daughter)
So, if the couple were to have a son, the father can only pass down the Y chromosome. Therefore, their son cannot be affected by the father's Xh
However, the mother has one Xh chromosome, so there is 50% chance of her passing it down to the son.
A daughter gets an X chromosome from her mother and an X chromosome from her father. Suppose X chromosome from her mother has the gene for normal blood clotting and X chromosome from her father has the gene for hemophilia, then the daughter will not have hemophilia since the normal blood clotting gene from her mother is dominant. So, she will be a carrier of hemophiliaand will pass on to her children.
So, the answer is 50% and 0 ,which is (B)
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