Question

Explain how , offsprings and parents of organisms reproducing sexually have the same number of chromosomes.

Answer 1

when the process of making of gametes starts the chromosomes number remains half in the sperms/ova.so when fertilisation occurs the chromosomes numbers restored (2n).
hope it helps.

Answer 2

offsprings have same chromosomes because the germ cells undergoes meosis and its number reduces to half.