Question

why DNA of a parent don't match exact to their children???

Answer 1

a child has two parents.Therefore a mix of their parents or their grandparents DNA which was recessive in their parents may pass on to them

Answer 2

because in humans there are 23 pairs of chromosomes in each cell. in one pair one characteristics is of male parent and other one is of female parent.when there is genetic recombination characteristics are exchanged