What is the effect of DNA copying, which is not perfectly accurate, on the reproduction process?

What is the effect of DNA copying, which is not perfectly accurate, on the reproduction process ? How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals ?

(i) DNA copying leads to more variations in the offspring.
(it) Sexually reproducing organisms have special lineage of cells which have only half the amount of DNA/ half the number of chromosomes as the parent cell.
(iii) When such germ cells fused, a new individual is formed with the same amount of DNA as that of parent.