Question

Which one ensure maintenance of chromosome number generation after generation?

Answer 1

The number of chromosomes in each generation are maintained due to meiosis. The meiosis is a kind of reductive division. When gametes are formed by meiosis, the number of chromosomes are halved. Hence each gamete will have only one pair of chromosome.

Later the haploid gamete will fuse with the complementary haploid gamete and form Diploid Zygote(2n). Hence the number of chromosomes are maintained.

For more details you can view my old answers regarding S-phase, certain stages of meiosis etc. If still you have doubts, you can ask anytime or you can refer Molecular cell biology by Bruce Alberts.