Mendelian Disorders
Read the following passage carefully and answer the given questions.
Genetic disorders may be grouped into two categories – Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in a single gene. These disorders are transmitted to the offspring on the same lines as in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle-cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc. The Mendelian disorders may be dominant or recessive. By pedigree analysis, one can easily understand whether the trait in question is dominant or recessive. Similarly, the trait may also be linked to the sex chromosome or an autosome.
α-thalassemia is controlled by the genes:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → HBA1 and HBA2 on chromosome 16 of each parent
Thalassemia is an autosome-linked recessive blood disease. The body makes too few globin chains, either alpha or beta, for haemoglobin. The more genes are affected, the fewer alpha globin molecules are made. β-Thalassemia is controlled by a single gene, HBB, on chromosome 11.
(1) HBB and HB1 on chromosome 11 of each parent — Incorrect. HBB on chromosome 11 controls β-thalassemia. There is no gene called HB1 in this disease.
(2) HAA1 and HAB1 on chromosome 16 of each parent — Incorrect. The chromosome is right, but these gene names do not exist. The genes are HBA1 and HBA2.
(3) HBA1 and HBA2 on chromosome 16 of each parent — Correct. They are the two linked genes of α-thalassemia.
(4) HBB and HAA on chromosome 11 of each parent — Incorrect. HBB controls β-thalassemia, and there is no gene called HAA.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Mendelian Disorders – “… In α Thalassemia, production of α globin chain is affected while in β Thalassemia, production of β globin chain is affected. α Thalassemia is controlled by two closely linked genes HBA1 and HBA2 on chromosome 16 of each parent and it is observed due to mutation or deletion of one or more of the four genes.”