Sickle-cell anaemia is an autosomal linked recessive disease that can be transmitted from parents to the offspring when both the partners are carrier or heterozygous. The disease is controlled by a single pair of allele, \(Hb^A~ and~ Hb^S.\)
Identify X, Y and Z.

Autosomal recessive disorder- We carry two copies of genes, from our mother, and one copy from our father. In the case of autosomal recessive genetic disease, both copies suffer a mutation that will make the gene behave abnormally. Example: - Sickle cell anaemia. Sickle cell anaemia is an inherited RBC (red blood cell) disorder in which there is not plenty of RBC available to transport oxygen through the body as their normal free-flowing biconcave shape is distorted to an abnormal sickle shape. As this disease is an autosomal recessive disorder, so it can only express itself in the homozygous condition. When it is present in the heterozygous state, it can only work as a carrier. The sixth position of the haemoglobin at the site of beta chain amino acid glutamine is replaced with valine, this is the main cause of the disease. So, the Z will be Valine and the normal Hb gene has CTC which is converted to CAC, & GAG will be converted to GTG in the diseased sickle cell.

Hence, the correct answer is option “B” – CAC GTG val (GUG).