Analyse the events during every stage of cell cycle and notice how the following two parameters change:
number of chromosomes (N) per cell
The number of chromosomes (N) remains constant throughout the cell cycle. During G₁ phase, the cell has its normal chromosome number. During S phase, although chromosomes duplicate, the chromosome count does not change as sister chromatids are still considered part of the same chromosome. During G₂ phase, the chromosome number remains unchanged. During M phase (mitosis), which is called equational division, the number of chromosomes in parent and progeny cells remains the same. Even during anaphase when sister chromatids separate, each daughter cell receives the same number of chromosomes as the parent cell.
amount of DNA content (C) per cell
The amount of DNA content (C) changes during the cell cycle. During G₁ phase, the DNA content remains at its basic level. During S phase, DNA replication occurs, and the DNA content doubles. During G₂ phase, the doubled DNA content is maintained as the cell prepares for division. During M phase, after karyokinesis and cytokinesis are complete, the DNA content in each daughter cell returns to the original level, as the duplicated DNA is equally distributed between the two daughter cells.
Explanation
This question tests understanding of the distinction between chromosome number and DNA content. The key concept from the textbook is that mitosis is 'equational division' - chromosome number remains constant. However, DNA content fluctuates: it doubles during S phase due to DNA replication, then halves after cell division. Students should understand that chromosome duplication in S phase doesn't increase chromosome number (N) because sister chromatids remain attached and are counted as one chromosome until anaphase separation.