Question

A man and 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

Answer 1

Hint: The mode of inheritance of such diseases is through chromosomes that are responsible for determining the gender of humans. Haemophilia is an example of this type of disease. Barr’s body is related to this specific type of chromosome.

Complete answer:
The sex-linked recessive inheritance is the passing down of mostly X-chromosome from the female parent which is a carrier and will not show any signs of the disease will pass the chromosome to the male offspring and few of them will be affected while few of them will be a carrier.

Additional Information:
-When the gene or chromosomal mutation occurs on a sex chromosome then the pattern of its inheritance and arrangement will be known as sex-linkage.
-The sex chromosomes are of two types: X-chromosome and Y-chromosome.
-The disease may be X-linked recessive, X-linked dominant, and Y-linked depending upon the presence of the chromosome.
-The sex-linked disease depends upon the sex of the parent and that of the child.
-X-linked is the most commonly occurring disease.
-The females mostly carry an abnormal or affected one X-chromosome which will make them a carrier of the disease.
-The female will pass this down to their male offspring as they will have only one X-chromosome.
-The female offspring will not be affected or will be a carrier as they have two X-chromosomes from both the parents.
-Few examples of sex-linked recessive disorders are color-blindness, muscular dystrophy, etc.

So, the correct answer is, “Sex-linked recessive.”

Note: The fraction of the percentage of effectiveness depends upon the composition of the chromosomes. The male offspring with a carrier mother and unaffected father will have a 50% chance of being affected or normal while female offspring will have a 50% chance of being a carrier or normal because the X-chromosome of the mother will be inherited by the son only.