Myotonic dystrophy is an/a -

The correct answer is Option (2) → Autosomal dominant trait

Myotonic dystrophy is a Mendelian disorder that affects the muscles. Its gene is on an autosome (a chromosome other than X and Y), and the faulty allele is dominant, so one copy is enough to cause it. In a pedigree, such a trait shows in every generation, affects males and females alike, and an affected child has at least one affected parent.

Option (1) Autosomal recessive trait — Incorrect. A recessive disorder shows only when both copies of the allele are faulty, and it can skip generations. The book’s example is sickle-cell anaemia.

Option (2) Autosomal dominant trait — Correct. NCERT gives myotonic dystrophy as its example of an autosomal dominant trait in pedigree analysis.

Option (3) Sex-linked recessive disorder — Incorrect. Sex-linked recessive disorders have their gene on the X chromosome and show mostly in males, as in haemophilia and colour blindness.

Option (4) Sex-linked dominant disorder — Incorrect. The gene for myotonic dystrophy is not on a sex chromosome, so it is not sex-linked.

NCERT Extract:
Pedigree Analysis – …