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.
Which one of the following diseases is an autosomal dominant disorder?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Myotonic dystrophy
A Mendelian disorder is called autosomal dominant when its gene lies on an autosome and one copy of the changed allele is enough to cause the disease. Such a trait usually appears in every generation of a pedigree. In an autosomal recessive disorder, both copies of the gene must be changed.
(1) Sickle-cell anaemia — Incorrect. It is an autosome-linked recessive trait. A person is affected only when both the alleles are HbS.
(2) Myotonic dystrophy — Correct. It is an autosomal dominant trait, so a single changed allele on an autosome causes it.
(3) Phenylketonuria — Incorrect. It is an autosomal recessive trait.
(4) Thalassemia — Incorrect. It is an autosome-linked recessive blood disease.
Note 1: 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.
Note 2: A similar question was also asked in CUET (UG) 2026 on 06-06-2026 (Slot 1) and on 19-05-2026 (Slot 1).