Match List-I with List-II
| List-I | List-II |
|---|---|
| Disorders | Features |
| (A) Colour blindness | (I) Autosomal dominant |
| (B) Sickle-cell anaemia | (II) Trisomy of chromosome 21 |
| (C) Myotonic dystrophy | (III) Sex-linked recessive |
| (D) Down’s Syndrome | (IV) Autosome linked recessive |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) - (III), (B) - (IV), (C) - (I), (D) - (II)
(A) Colour blindness — this matches (III) Sex-linked recessive. The genes for red and green colour vision lie on the X chromosome. A male has only one X, so one defective allele is enough to show the disorder.
(B) Sickle-cell anaemia — this matches (IV) Autosome linked recessive. A single pair of alleles on an autosome controls it. Only a person with two sickle alleles (HbSHbS) shows the disease.
(C) Myotonic dystrophy — this matches (I) Autosomal dominant. It is the example NCERT gives for an autosomal dominant trait. One defective allele on an autosome is enough to show it.
(D) Down’s Syndrome — this matches (II) Trisomy of chromosome 21. The cells carry an extra copy of chromosome 21, so there are 47 chromosomes instead of 46. It is a chromosomal disorder, not a single-gene one.