Question

Match the human genetic disorder with the causative abnormal chomosome.

(a)	Sickle cell anaemia	1.	Sex linked (X-chromosome)
(b)	Colour blindness	2.	Autosomal chromosome 7
(c)	Phenylketonuria	3.	Autosomal chromosome 11
(d)	Cystic fibrosis	4.	Autosomal chromosome 4
(e)	Huntington's disease	5.	Autosomal chromosome 12

• A. a- 3, b- 5, c- 1, d- 2, e- 4
• B. a- 5, b- 1, c- 2, d- 3, e- 4
• C. a- 4, b- 1, c- 5, d- 2, e- 3
• D. a- 3, b- 1, c- 5, d- 2, e- 4
• E. a- 2, b- 1, c- 5, d- 3, e- 4

Answer 1

Answer: (D)

a- 3, b- 1, c- 5, d- 2, e- 4

A mutation in Hb${}^b$ gene, a $\beta$-chain gene, causes replacement of A by T at the 17${}^{th}$ nucleotide of the Hb${}^b$ gene changes the codon GAG (glutamic acid) to GTG (which encodes valine). The mutated allele Hb${}^s$ encodes the abnormal haemoglobin molecules which stick to one another and cause stiffness and sickle shape of red blood cells, sickle cell anaemia. The haemoglobin-$\beta$-gene is located on chromosome 11. Phenylketonuria is an inborn error of metabolism that results in an inability of break down the amino acid called phenylalanine. It is caused by a mutation in PAH gene, present on chromosome 12, responsible for an enzyme called as phenylalanine hydroxylase.

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

Cystic fibrosis is caused by mutation in CFTR gene, present on long (q) arm of chromosome 7, that codes for chloride channels.

Colour blindness is a genetic disorder because the governing genes are present of X-chromosome which is a sex chromosome in human. The trait is transmitted to offspring in a sex linked manner from mother to son and from father to daughters.

Thus, the correct answer is option D.