A human body cell in interphase has 46 chromosomes before DNA replication. What are the chromosome number and the number of DNA molecules at the start of mitosis, after replication?
Answer and explanation
Correct answer: A. The chromosome number is unchanged and there are 92 DNA molecules
- Step 1: Replication copies each DNA molecule, but the two copies stay joined at the centromere as chromatids. Step 2. So the chromosome number (counted by centromeres) is unchanged, while the DNA content doubles from 46 to 92 molecules. Answer: unchanged chromosome number and 92 DNA molecules. Why not the others: Chromatids are not counted as separate chromosomes until they separate; unreplicated cells would have 46 DNA molecules; and halving happens only in meiosis.
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