Normal cell division — Mitosis:

Mitosis is the process of cell division that enables organisms to maintain cell populations and grow. All chromosomes duplicate themselves prior to cell division, followed by partitioning of these exact copies into daughter cells. In the image to the right, two sets of chromosomes are going through mitosis.

Sexual cell division — Meiosis:

In contrast, meiosis is a two-part cell division process which results in reproductive cells (eggs and sperm) with one-half the number of chromosomes of the parent cell.

In males, the process results in four equal gametes with one chromosome each (sperm cells—not shown). In females, each ovum is produced by two chromosome divisions, called the first and second meitic divisions, and the parent cell's cytoplasm and organelles end up in one gamete.

When a haploid sperm cell fertilizes a haploid ovum, a diploid zygote is formed, with one set of chromosomes donated from each parent.

Triploid organisms are created using a third, distinct process. To learn more about this process, see Development of Induced Triploidy and Development of Natural Triploidy