Question

how does the amount of DNA remain constant through each new generation in a combination of DNA copies of two individuals

Answer 1

The Haploid nature of gametes is responsible for the DNA being constant in the new individual. That is the gametes doesn't contain 23 pairs(46) of chromosomes instead they have only 23 chromosomes. Hence when dna of two gametes combine it remains constant

Answer 2

i think this is the correct answer.