The syndrome caused by the presence of an additional copy of chromosome number 21 is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Down’s Syndrome
An aneuploidy is the gain or loss of a chromosome, which happens when chromatids fail to separate during cell division. The gain of an extra copy of chromosome 21 is called trisomy 21.
(1) Myotonic dystrophy — Incorrect. This is a muscle disease that is caused by a change in a single gene. It is not caused by an extra chromosome.
(2) Down’s Syndrome — Correct. The person has an extra copy of chromosome 21, so there are 47 chromosomes in all.
(3) Klinefelter’s Syndrome — Incorrect. The person has an extra X chromosome, so the sex chromosomes are XXY.
(4) Turner’s Syndrome — Incorrect. One X chromosome is missing in the female, so the sex chromosomes are XO.
Note: A similar question was also asked in CUET (UG) 2023 on 23-06-2023 (Slot 3).
NCERT Extract:
Chromosomal Disorders – …
