Which one of the following disorders is an example of an autosomal dominant trait?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Myotonic dystrophy
A Mendelian disorder is autosomal when the gene is on a non-sex chromosome. It is dominant when one changed allele is enough to show the disorder. It is recessive when both alleles must be changed.
(1) Sickle-cell anaemia — Incorrect. It is an autosome-linked recessive disorder. It is caused by a change of one base in the gene for the β-globin chain.
(2) Phenylketonuria — Incorrect. It is an autosomal recessive disorder. The enzyme phenylalanine hydroxylase is missing.
(3) Myotonic dystrophy — Correct. It is the example of an autosomal dominant trait in the pedigree analysis.
(4) Thalassemia — Incorrect. It is an autosome-linked recessive disorder. Too few globin molecules are made.
Note: A similar question was also asked in CUET (UG) 2026 on 19-05-2026 (Slot 1).