Question

Number of chromosomes in maize root cells at G1 phase, after S and M phases respectively

• A. 20, 20, 20
• B. 20, 40, 20
• C. 20, 10, 20
• D. 20, 40, 40

Hint:

Remember that in mitotic division, the chromosome number does not change; it remains the same after DNA replication (S phase) and during cell division (M phase).

Answer 1

The Correct Option is A

Chromosome Number in Maize Root Cells

In maize root cells:

• G1 Phase: At the G1 phase, the cell contains the full set of chromosomes, which is 20 in this case.
• S Phase: During the S phase, DNA replication occurs, and the chromosomes duplicate. However, the chromosome number in the cell remains 20, as each chromosome has only replicated into two sister chromatids, still counted as one chromosome each.
• M Phase (Mitosis): During mitosis, the chromosomes are segregated into two daughter cells, maintaining the same chromosome number, which remains 20 in both daughter cells.

Thus, the number of chromosomes at each stage (G1, after S, and after M) in maize root cells is:

20, 20, 20

The correct answer is (1) 20, 20, 20.