Question

why the amount of dna does get doubled ?

Answer 1

THE AMOUNT OF DNA NEVER GETS DOUBLED 

Answer 2

Mitosis is the fundamental process by which most life forms grow and reproduce. Commonly referred to as cell division, mitosis occurs when one cell divides into two cells that have the same number of chromosomes as the parent cell. Mitosis is the primary form of reproduction for unicellular organisms, and it is the means of growth and regeneration for multicellular organisms. DNA, which must be passed to the resulting cell, is replicated during a preparatory period known as interphase. The S-phase portion of interphase is when the DNA content of a cell increases. Ordinarily, a cell has one set of chromosomes, which are thread-like structures that contain the cell's DNA. During the G 1 phase, each chromosome contains one molecule of DNA. But when the reproductive process begins, the cell will need two sets of DNA: one for itself and one for the offspring cell. During the S phase, the cell replicates its genetic material so that each chromosome will contain two molecules of DNA. Thus, upon completion of the S phase, the cell has the same number of chromosomes, but its DNA content has doubled.