cell with half the usual number of chromosomes

Haploid is the term used when a cell has half the usual number of chromosomes. A normal eukaryote organism is composed of diploid cells, one set of chromosomes from each parent. However, after meiosis, the number of chromosomes in gametes is halved. That is the haploid condition.

In humans, the diploid number of chromosomes is 46 (2x23). The number in haploid cells (sperm and eggs) is 23. Some types of animals are haploid, such as male Hymenoptera (ants, bees and wasps). This is a special genetic system called haplodiploidy.

Some plants and animals are polyploid, with more than two sets of chromosomes. For example, one species of wheat is hexaploid, with six sets of chromosomes, although other species of wheat have only two sets. Because so many organisms are diploid, it can become confusing whether haploid refers to one set of chromosomes or more than one. The special term monoploid can be used; it means one set of chromosomes.

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