Which of the following statements is correct about sickle-cell anaemi…

The correct answer is Option (4) → All of these.

Sickle-cell anaemia and thalassemia are both Mendelian disorders of haemoglobin, the protein made of globin chains that carries oxygen in red blood cells. They differ in what goes wrong with the globin.

Option (1) Thalassemia is a quantitative problem of synthesising too few globin molecules. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. In thalassemia, a mutation or deletion reduces the rate of synthesis of the α or β globin chain. Too few globin molecules are made, so the problem is one of quantity.

Option (2) Sickle-cell anaemia is a qualitative problem of synthesising an incorrectly functioning globin. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. In sickle-cell anaemia, enough globin is made, but one amino acid in the β chain is changed (glutamic acid to valine). The globin is made wrongly, so the problem is one of quality.

Option (3) Both are autosome-linked recessive blood diseases transmitted from parents to the offspring when both the partners are unaffected carriers for the gene (heterozygous). — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Both disorders are autosome-linked recessive. A child gets the disease when both parents are unaffected carriers (heterozygous) and each passes on the mutant allele.

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. … Thalassemia differs from sickle-cell anaemia in that the former is a quantitative problem of synthesising too few globin molecules while the latter is a qualitative problem of synthesising an incorrectly functioning globin.”
Mendelian Disorders – “… Sickle-cell anaemia : This is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous).”