MCAT Biology Question 25: Answer and Explanation
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Question: 25
10. Which of the following does NOT likely contribute to genetic variability?
- A. Random fertilization of an egg by a sperm
- B. Random segregation of homologous chromosomes
- C. Crossing over between homologous chromosomes during meiosis
- D. Replication of the DNA during S stage
Correct Answer: D
Explanation:
The safest way to answer this question correctly is to go through each answer choice and eliminate the ones that contribute to genetic variability. The random fertilization of a sperm and an egg, the random segregation of homologous chromosomes during anaphase I, and crossing over between homologous chromosomes during prophase I all contribute to genetic variability during sexual reproduction because they result in novel combinations of genetic material, eliminating choices (A), (B), and (C). S stage, choice (D), should specifically not cause increased genetic variability; the DNA should be copied precisely, without error, meaning that both strands of DNA should be identical.