Which of the following pairs is correctly matched?

The correct answer is Option (2) → Thalassemia – Reduced rate of synthesis of one of the globin chains

Genetic disorders fall into two groups. Mendelian disorders come from a change in a single gene, such as haemophilia, sickle-cell anaemia and thalassemia. Chromosomal disorders come from the absence, excess or wrong arrangement of chromosomes, such as Down's syndrome.

Option (1) Haemophilia – Autosomal recessive disorder — Incorrect. Haemophilia is a sex-linked recessive disorder. Its gene is on the X chromosome, which is why it passes from carrier mothers to sons.

Option (2) Thalassemia – Reduced rate of synthesis of one of the globin chains — Correct. In thalassemia a mutation or deletion lowers the rate of synthesis of one of the globin chains (α or β). Too few globin molecules are made, which leads to anaemia.

Option (3) Down’s syndrome – Mendelian disorder caused by a single gene mutation — Incorrect. Down's syndrome is a chromosomal disorder caused by an extra copy of chromosome 21 (trisomy 21). It is not caused by a single gene mutation.

Option (4) Sickle-cell anaemia – Valine replaced by glutamic acid in the β-globin chain — Incorrect. The pair is reversed. In sickle-cell anaemia glutamic acid is replaced by valine at the sixth position of the β-globin chain.

NCERT Extract:
Mendelian Disorders – “… Thalassemia : This is also an autosome-linked recessive blood disease transmitted from parents to the offspring when both the partners are unaffected carrier for the gene (or heterozygous). The defect could be due to either mutation or deletion which ultimately results in reduced rate of synthesis of one of the globin chains (α and β chains) that make up haemoglobin.”
Mendelian Disorders – “… Haemophilia : This sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied.”
Mendelian Disorders – “… The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule.”
Chromosomal Disorders – “… Down’s syndrome, Turner’s syndrome, Klinefelter’s syndrome are common examples of chromosomal disorders.”