Solution:

• Yes, DNA replication can occur throughout the G1 phase of the cell cycle. Each chromosome is made up of one chromatid, and the number of chromosomes remains constant. The chromosome is generated in the S phase by the joining of two sister chromatids at the centromere. In the G2 phase, similar conditions persist, whereas in the M phase, sister chromatids split and migrate to distinct cells. In mitosis, the number of chromosomes remains constant.
•  During the G1 phase, the amount of DNA in the cell remains constant, but during the S phase, it doubles as DNA replication occurs. In the G2 phase of the cell cycle, it is doubled, but in the M phase, it is halved.