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Step-by-Step Solution
Step 1: Understanding the Context
The fruit fly (Drosophila melanogaster) has a diploid number of 8 chromosomes, meaning 2n = 8. In a typical cell cycle, G1, S, and G2 phases together form the interphase, followed by mitotic division.
Step 2: Chromosome Number During G1 Phase
During G1 phase (the “gap” phase after cell division), the cell has 8 chromosomes. Each chromosome is in its single chromatid state, but there are 8 distinct chromosomes.
Step 3: Changes in S Phase
During the S phase (the “synthesis” phase), the DNA content doubles because each chromosome replicates its DNA. However, each chromosome is still counted as a single chromosome, even though it now has two sister chromatids.
Step 4: Chromosome Number After S Phase
Because the number of chromosomes is counted based on the presence of a functional centromere rather than on the amount of DNA, the total chromosome count remains 8 chromosomes. Though the DNA amount doubles, this does not alter the chromosome count.
Conclusion
The number of chromosomes remains 8 even after the S phase.
