DNA replication in chicken cells before mitosis

Steps:

• Chickens have 78 diploid chromosomes in body cells.
• DNA replicates in S phase of interphase, before mitosis begins.
• At prophase start, each of the 78 chromosomes consists of two sister chromatids.
• Each chromatid is one DNA molecule, yielding 78 × 2 = 156 DNA molecules.

Why D is correct:

• Post-replication in prophase, the diploid number of chromosomes (78) doubles to 156 DNA molecules per the definition of sister chromatids.

Why the others are wrong:

• A: Matches human diploid chromosomes (46), not chicken (78).
• B: Equals chicken chromosome number before replication.
• C: Exceeds replicated total; no biological basis in chicken cells.

Final answer: D