Early Prophase Chromosome DNA Strands

Steps:

• DNA replicates in S phase, so chromosomes enter mitosis with two sister chromatids each.
• Prophase begins with chromosome condensation from chromatin threads.
• Each chromatid contains one DNA double helix composed of two antiparallel strands.
• One chromosome thus has two chromatids, totaling four DNA strands.

Why B is correct:

• B. 4 aligns with the definition of a duplicated chromosome having two chromatids, each with a double-stranded DNA molecule.

Why the others are wrong:

• A. 2: Counts chromatids, not individual DNA strands.
• C. 1: Applies to unreplicated G1 chromosomes with one chromatid.
• D. 2: Duplicates A, undercounting total strands.

Final answer: B