Question

(a) In the control sample histogram, identify the phase of the cell cycle (G1, S, or G2) of the population of cells in each region delineated by vertical lines. Label the histogram with these phases and explain your answer. (b) Does the S phase population of cells show a distinct peak in the histogram? Why or why not?

Short answer

(a) According to the diagram, A, B, and C are intervals in which cells are grown in culture, and G1, G2, and S phases occur in a sequential manner. So interval A shows the G1 phase, interval B shows the S phase, and interval C shows the G2 phase.

(b) As the S phase progresses, the DNA content in each cell changes. Thus, here the cells in the S phase are showing different levels of fluorescence.

Step-by-step solution

Step 1:Cell cycle

The cell cycle is a collection of sequential steps by which cells divide to produce two daughter cells. It completes in four phases that are G1, S, G2, and M. G1 is the first phase at which cells do all preparations for division.

In the S phase, the cell replicates its DNA. In the G2 phase, cells are prepared to divide. M phase is a dividing phase.

Explanation for answer (a)

Cells are inhibited from dividing in interval A when they start their cell cycle. The cell cycle initiates from G1 and then to S, and after it, they reach in G2 phase.So in interval A, G1 is the phase, and interval B indicates the S phase, and C shows the G2 phase.

Explanation for answer (b)

The cells in the S phase do not show a distinct peak in the histogram because the DNA content varies in each cell as it progresses to divide. Due to different levels of fluorescence in each cell, the peak is not formed distinct.