<P> Dihaploid and polyhaploid cells are formed by haploidisation of polyploids, i.e., by halving the chromosome constitution . </P> <P> Dihaploids (which are diploid) are important for selective breeding of tetraploid crop plants (notably potatoes), because selection is faster with diploids than with tetraploids . Tetraploids can be reconstituted from the diploids, for example by somatic fusion . </P> <P> The term "dihaploid" was coined by Bender to combine in one word the number of genome copies (diploid) and their origin (haploid). The term is well established in this original sense, but it has also been used for doubled monoploids or doubled haploids, which are homozygous and used for genetic research . </P> <P> Euploidy is the state of a cell or organism having one or more than one set of the same set of chromosomes, possibly excluding the sex - determining chromosomes . For example, most human cells have 2 of each of the 23 homologous monoploid chromosomes, for a total of 46 chromosomes . A human cell with an extra set out of the 23 normal ones would be considered euploid . Euploid karyotypes would consequentially be a multiple of the haploid number, which in humans is 23 . Aneuploidy is the state where one or more chromosomes of a normal set are missing or present in more than their usual number of copies . Unlike euploidy, aneuploid karyotypes will not be a multiple of the haploid number . In humans, examples of aneuploidy include having a single extra chromosome (such as Down syndrome), or missing a chromosome (such as Turner syndrome). Aneuploid karyotypes are given names with the suffix - somy (rather than - ploidy, used for euploid karyotypes), such as trisomy and monosomy . </P>

The term used to refer to this full complement of chromosomes is the