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A man and a woman, who do not show any apparent signs of a certain inherited disease, have seven children (2 daughters and 5 sons). Three of the sons suffer from the given disease but none of the daughters are affected. Which of the following modes of inheritance do you suggest for this disease
A
Sex-limited recessive
B
Autosomal dominant
C
Sex-linked recessive
D
Sex-linked dominant
Detailed Solution
The parents are both unaffected, but some children are affected, so the disease is recessive; a dominant disease would appear in at least one parent.
Only sons are affected and the daughters are normal, which points to a sex-linked (X-linked) recessive trait.
The mother must be a carrier ($X^aX$) and the father normal ($XY$).
Each son receives his only X chromosome from the mother, so half the sons are expected to be affected ($X^aY$); here 3 out of 5 sons are affected.
The daughters receive the father's normal X, so none of them is affected (half of them are carriers).
So the suggested mode of inheritance is sex-linked recessive (like haemophilia).
Only sons are affected and the daughters are normal, which points to a sex-linked (X-linked) recessive trait.
The mother must be a carrier ($X^aX$) and the father normal ($XY$).
Each son receives his only X chromosome from the mother, so half the sons are expected to be affected ($X^aY$); here 3 out of 5 sons are affected.
The daughters receive the father's normal X, so none of them is affected (half of them are carriers).
So the suggested mode of inheritance is sex-linked recessive (like haemophilia).