When are chromosomes (dna) copied?​

Interphase begins with G1 (G stands for gap) phase. During this phase, the cell makes a variety of proteins that are needed for DNA replication. During S phase, which follows G1 phase, all of the chromosomes are replicated. Following replication, each chromosome now consists of two sister chromatids.

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Chromosome replication

Explanation:

Chromosome replication is a key event during the cell cycle that must be completed before a cell divides. To reproduce successfully, every cell must replicate its chromosome and distinguish these sister chromosomes from one another.

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genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).