Replicated Chromosome Structure in Prophase of Mitosis

Steps:

• DNA replication in S phase produces two identical DNA double helices, each with 2 polynucleotide strands, totaling 4 strands per chromosome.
• In prophase, the chromosome condenses into a structure with two centromeres (one per attached half) and two telomeres at the ends.
• The attached halves are not counted as separate chromatids until anaphase, so chromatids number 0.
• This configuration prepares the chromosome for alignment in metaphase.

Why B is correct:

• By definition, a replicated chromosome in prophase has 2 centromeres joining the halves, 4 polynucleotide strands from duplication, 2 telomeres, and 0 distinct chromatids as they remain fused.

Why the others are wrong:

• A: Underestimates replication effects, showing pre-S phase counts (1 centromere, 2 strands, 0 chromatids).
• C: Not enough information (option incomplete).
• D: Wrongly assigns 2 chromatids (separation occurs later) and 2 strands (ignores replication doubling to 4), with excess 4 telomeres.

Final answer: B