Assertion [A]: Only a boy child could be born with the substitution of glutamic acid by valine on the 6th position of haemoglobin chain.

Reason [R]: The gene for the above mutation occurs in Y chromosome.

The correct option is D Both A and R are false.

• Sickle-cell anaemia arises due to gene mutation in the autosomes. It doesn't affect either of the sex chromosomes (X or Y).
• It can be transmitted from parents to the offspring when both the partners are carriers for the gene or are suffering from the disease. Only homozygous individuals show the diseased phenotype.
• In sickle-cell anaemia the RBCs become sickle-shaped. It is caused due to the replacement of glutamic acid by valine at the 6th position of the haemoglobin chain.