When and how does the amount of dna (c-content; where c
isthe quantity of dna in a haploid genome) in a cell's nucleus
changein the course of the cell cycle?

G1 phase: 2C

S phase: 4C

G2 phase: 4C

Meiosis-I: 2C and Meiosis-II: C

Mitosis: 2C

Explanation:

Let's suppose that a cell with 2C DNA content enters the cell cycle. As the G1 cell with 2C content would enter the S phase, DNA replication would double the amount of DNA. Therefore, the cell by the end of the S phase and in the G2 phase would have 4C DNA.

If the G2 cell with 4C DNA enters meiosis-I, separation of homologous chromosomes to the opposite poles in anaphase-I would reduce the DNA content to 2C. Therefore, the cell by the end of anaphase-I would have 2C content. Meiosis-II would further reduce the DNA content in anaphase-II by separation of sister chromatids to opposite poles. Therefore, each of the four daughter cells formed by the end of meiosis would have C DNA content.

If the G2 cell with 4C DNA enters mitosis, separation of sister chromatids to opposite poles in anaphase would reduce the DNA content. Therefore, each of the two daughter cells formed by the end of mitosis would have 2C DNA content.