Question

Match the genetic disorders in Column I to the corresponding underlying cause in Column II.

Column I	Column II
P. Klinefelter Syndrome	1. X-chromosome insufficiency
Q. Turner syndrome	2. DNA helicase mutations
R. Bloom syndrome	3. Nucleotide excision repair defects
S. Xeroderma pigmentosum	4. Extra X chromosome(s) in a male

• A. P-1; Q-3; R-4; S-2
• B. P-4; Q-1; R-2; S-3
• C. P-4; Q-2; R-3; S-1
• D. P-3; Q-2; R-4; S-1

Hint:

Klinefelter is an extra X in a male, Turner is a single X, Bloom is a helicase defect, and Xeroderma pigmentosum is a repair defect; check this against the given options.

Answer 1

The Correct Option is B

This question matches four genetic disorders to their real underlying molecular cause. Go through each disorder in Column I and match the description in Column II that correctly explains it.

1. P. Klinefelter Syndrome: this condition affects males who carry one or more extra X chromosomes (karyotype 47,XXY in the common form). So it is a case of an extra X chromosome in a male, which is description 4.
2. Q. Turner syndrome: this condition affects females who have only one functional X chromosome (karyotype 45,X, a monosomy of the X chromosome), instead of the usual two. That is exactly an insufficiency (shortage) of X chromosome material, which is description 1.
3. R. Bloom syndrome: this is caused by mutation of the BLM gene, which encodes a RecQ family DNA helicase needed to unwind DNA correctly during replication and repair. Loss of this helicase causes the genome instability seen in Bloom syndrome, so this matches description 2 (DNA helicase mutations).
4. S. Xeroderma pigmentosum: this is caused by mutations in genes of the nucleotide excision repair (NER) pathway (the XP genes), which normally remove bulky, UV-induced DNA lesions. A defective NER pathway leaves these lesions unrepaired, causing extreme UV sensitivity and a high skin cancer risk. This matches description 3 (nucleotide excision repair defects).

Putting these four matches together gives P-4, Q-1, R-2, S-3, which is option (B) among the four choices listed here.

Let's summarize:

• Klinefelter syndrome: extra X chromosome in a male.
• Turner syndrome: single X chromosome (X insufficiency) in a female.
• Bloom syndrome: BLM helicase gene mutation.
• Xeroderma pigmentosum: nucleotide excision repair gene defect.

So the correct match is P-4; Q-1; R-2; S-3, which is option (B).