The genetic disorder caused due to presence of an additional copy of the chromosome number 21 is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Down's syndrome
Option (1) Down's syndrome — Correct. It is trisomy of chromosome 21, so the person has 47 chromosomes.
Option (2) Klinefelter syndrome — Incorrect. It is caused by an extra X chromosome in a male (44 + XXY).
Option (3) Turner's syndrome — Incorrect. It is caused by the loss of one X chromosome in a female (44 + X0).
Option (4) Haemophilia — Incorrect. Haemophilia is a sex-linked recessive Mendelian disorder, caused by a faulty gene, not by an extra chromosome.
Note: A similar question was also asked in CUET (UG) 2026 on 29-05-2026 (Slot 1).
NCERT Extract:
Chromosomal Disorders – “… Down’s Syndrome : The cause of this genetic disorder is the presence of an additional copy of the chromosome number 21 (trisomy of 21). This disorder was first described by Langdon Down (1866). The affected individual is short statured with small round head, furrowed tongue and partially open mouth (Figure 4.16).”
Figure 4.16 A representative figure showing an individual inflicted with Down’s syndrome and the corresponding chromosomes of the individual