Because it undergoes Mitosis where the chromosomes of a certain cell copies it's own and then split to form another cell or daughter cell. But note that only body cells act that way. Sex cells works differently that's why siblings don't look exactly the same even though they have the same parents. Only in mitosis where the quality and quantity are the same. but not in meiosis.
certainly rt-pcr is qualitative and can also theoretically be quantitative. anneal the rna to get a 1: 1 rna to dna copy, then proceed with quantitative pcr.
hope it helps! but im not really sure by this but you can try hehehehe sorry about that peace