1 Answer 1. The chromosomes copy at S phase. So S/G2 checkpoint up to early anaphase has 2n. You are on the right track to understanding the cell cycle, important to note the differences between homologous chromosomes (homologous pair) and sister chromatids, while understanding ploidy. During S (synthesis) phase which occurs between G1 and G2 , all the somatic DNA replicates.