Q.During which phase of interphase does DNA replication take place, so that the amount of DNA per cell doubles before the cell divides?

Interphase is the long, deceptively quiet-looking part of the cell cycle between one division and the next, during which a cell does almost all of its actual growth and preparation work; it typically occupies about 95% of the total cycle time. It is divided into three sub-phases. G1, the first gap phase, is when the cell grows by synthesising proteins, lipids and organelles while its DNA content remains at the unreplicated 2C level; G1 is heavily checkpoint-controlled, with a restriction point near its end deciding whether the cell commits to dividing or instead exits into G0. S phase, the synthesis phase, is when the entire genome is replicated, doubling the DNA content from 2C to 4C, while histone proteins are made to package the new DNA and the centrioles duplicate. G2, the second gap phase, is a further growth phase in which tubulin is synthesised into microtubules that will form the mitotic spindle, mitochondria and chloroplasts divide, and the protein Maturation Promoting Factor (MPF) is produced to trigger condensation of chromatin into visible mitotic chromosomes. The amount of DNA in a haploid nucleus at any point is measured as its C-value, so a cell's progress through interphase can be tracked as 2C (G1) through intermediate values (S) to 4C (G2 and mitosis).