Sexually-reproducing organisms make use of gametes to reproduce. The gametes are produced via the process of meiosis, which is a cell division that results in daughter cells (gametes) that have their chromosomal number reduced by half. A diploid (2n) organism i.e. possess two set of chromosomes undergoes meiosis to produce haploid (n) gametes i.e. contains one set of chromosomes. The male parent produces haploid sperm while the female parent produces haploid egg.
During reproduction, these haploid gametes (sperm and egg) combine in a process called FERTILIZATION to produce a diploid ZYGOTE. The diploid zygote then divides and grows into the full organism. Hence, since a zygote is formed by the fusion of two haploid gametes (sperm and egg), it contains a diploid chromosome number i.e. sperm (n) + egg (n) = zygote (2n)
