haploidejen

Haploidejen refers to haploid forms—cells or organisms carrying a single complete set of chromosomes. The haploid number, denoted n, contrasts with diploidy (2n). Haploides arise mainly through meiosis and, upon fertilization, join with another haploid to restore diploidy. In animals, the haploid phase is usually restricted to gametes; somatic cells are diploid. In plants, fungi, and many algae, haploid stages can be dominant or persistent, as in life cycles with alternation of generations.

Each haploid cell carries one allele per locus; genes on homologous chromosomes are not paired in the haploid state. Recombination during meiosis in the preceding diploid stage creates genetic diversity among the resulting haploid gametes. Haploids can also reproduce mitotically in some species, forming clonal haploid populations.

Haploidejen is a key concept in genetics and breeding. In research, haploid organisms such as Saccharomyces cerevisiae are valuable for genetic screens because recessive mutations are directly observable. In humans, haploid gametes have n=23; fertilization yields a diploid zygote with 46 chromosomes.

Terminology varies by language. Some use monoploidy to describe a single genome copy in certain organisms, but haploidy is the standard term in most contexts.