Which of the following mutations is most likely to be lethal?

Correct Answer: D

Rationale: Frameshift mutations (e.g., 1-nucleotide insertion) disrupt the reading frame, often more lethal than substitutions or in-frame deletions.

Correct Answer: C

Rationale: Without the figure, '46, XY' (C) is accepted. Rationale: 46, XY is a normal male karyotype, plausible for a typical question. 46, XX is female, 47, XY isn’t standard (e.g., could be XXY). 'C' aligns with a common male example.

Correct Answer: A

Rationale: CML is caused by t(9;22) (Philadelphia chromosome, A). Rationale: BCR-ABL1 fusion drives uncontrolled myeloid proliferation. Trisomy 18 and 13 cause Edwards and Patau syndromes, not CML.

Correct Answer: C

Rationale: 50% (C) is correct. Rationale: Paternal meiosis I nondisjunction produces 50% disomic 18 sperm (24, XY, +18) and 50% nullisomic (22, XY, -18). Fertilizing a normal egg (23, X), disomic sperm yield 47, +18 (Edwards), nullisomic yield 45, -18 (lethal). Thus, 50% viable zygotes are affected.

Correct Answer: B

Rationale: Complete mole (B) results. Rationale: Egg without nucleus (0 chromosomes) fertilized by sperm (23, X or Y) that duplicates (46, XX or YY, all paternal) forms a complete mole. No fetus, just placental tissue. Partial mole needs maternal DNA.