Question

Chromosomes duplicate during A–– and increase in number of chromosomes is observed first during B––. Fill the blanks correctly.

A. A – Interphase B – Prophase
B. A – S phase B – Telophase
C. A – Synthetic phase B – Gap2 phase
D. A – Interphase B - Anaphase

Answer 1

Chromosomes are duplicated during the S phase of interphase, and an increase in the visible number of chromosomes is first observed during telophase of mitosis. The correct option is (A).

Step-by-step explanation:

The student's question regarding chromosome duplication and the phases of the cell cycle can be answered with an understanding of interphase and the stages of mitosis. Chromosomes duplicate during the S phase of interphase, a process central to cellular replication and division. The correct option is A: A – S phase B – Telophase. The S phase, also known as the synthesis phase, is when each chromosome is replicated to produce two identical copies known as sister chromatids, which are held together at the centromere.

Though chromosomes are duplicated during the synthesis phase of interphase, an increase in the visible number of chromosomes (as sister chromatids) is first observed during telophase, when sister chromatids have reached the opposite poles of the cell and decondense, becoming individual chromosomes in the re-forming nuclei.