47 XYY occurs due to:

Correct Answer: C

Rationale: Paternal nondisjunction (C) causes 47, XYY. Rationale: Meiosis II nondisjunction in father produces YY sperm (24, YY), fertilizing X egg (23, X), yielding 47, XYY. Chimerism or UPD don’t fit; maternal nondisjunction gives XXY.

Correct Answer: A

Rationale: Beta satellite DNA is on the p-arm of acrocentric chromosomes (e.g., 13, 14, 15, 21, 22). 'A' is correct. Rationale: These repetitive sequences are near nucleolar organizer regions (NORs) on short arms, distinct from centromeric alpha satellites.

Correct Answer: D

Rationale: 69, YYY (D) cannot occur in triploidy. Rationale: Triploidy (3n=69) results from dispermy or diploid gametes (e.g., XXY, XXX), but YYY requires three Y-bearing sperms, biologically implausible in humans.

Correct Answer: A

Rationale: 1 maternal, 1 paternal set (A) is normal. Rationale: Diploidy (2n=46) requires 23 chromosomes from egg and sperm; deviations (B-D) cause moles or lethality.

Correct Answer: A

Rationale: Dispermy (A) causes 69, XYY. Rationale: Two Y-bearing sperms (23, Y each) + egg (23, X) yield triploid 69, XYY; nondisjunction or endomitosis don’t fit.