Question

Phenylketonuria, Huntington's disease and Sickle cell anaemia caused respectively due to disorders associated with

• A. Chromosome 7, chromosome 11 and chromosome 12
• B. Chromosome 11, chromosome 4 and chromosome 12
• C. Chromosome 7, chromosome 12 and chromosome 11
• D. Chromosome 4, chromosome 7 and chromosome 11
• E. Chromosome 12, chromosome 4 and chromosome 11

Answer 1

The correct option is E Chromosome 12, chromosome 4 and chromosome 11

Hemoglobin has four protein subunits, two $\alpha$-globin and two $\beta$-globin. The Hbb gene codes the $\beta$ chain. Missense mutation, replacement of A by T at the 17th nucleotide of the Hbb gene changes the codon GAG (glutamic acid) to GTG (which encodes valine). The mutated alllele Hbs encodes the abnormal hemoglobin molecules which stick to one another and cause stiffness and sickle shape of red blood cells. The sickle shaped RBC block and damage the vital organs and tissue. The hemoglobin-$\beta$ gene is located on chromosome 11.
Phenylketonuria is an inborn error of metabolism that results in inability to break down the amino acid called phenylalanine. It is caused by mutation in PAH gene, present on chromosome 12, responsible for an enzyme called phenylalanine hydroxylase, which breaks down phenylalanine into tyrosine.

Huntington's disease is an autosomal dominant disorder caused by mutation in HTT gene, located on the short (p) arm of chromosome 4, that codes for a protein called huntingtin. This is characterized by degradation of the nerve cells of brain.