haploidt

Haploidt is most commonly referred to by the standard term haploid, describing a cell, organism, or tissue that contains a single complete set of chromosomes (n). In contrast, a diploid (2n) has two homologous chromosome sets. Haploid genomes are typical of many gametes, spores, and some unicellular organisms, and they represent the unpaired chromosomal complement in a given life stage.

In nature, haploidy occurs in a variety of life cycles and lineages. In animals, haploid cells are typically restricted to gametes (sperm and eggs) within a predominantly diploid life cycle. In plants and algae, haploid stages can be more prominent: bryophytes (mosses, liverworts, hornworts) have a haploid dominant gametophyte generation, while seed plants generally exhibit a diploid dominant sporophyte generation but produce haploid pollen grains and ovules as part of their reproductive cycle. In fungi, many species are haploid for most of their life cycle, with brief diploid phases during sexual reproduction; some fungi also display a prolonged dikaryotic stage.

Genetically, haploid cells reveal recessive traits directly since there is no second allele to mask them. Meiosis is the primary process generating haploid gametes from diploid cells, and fertilization restores diploidy to form a zygote. Haploids are widely used in genetics and breeding because their simplified genotype can accelerate trait mapping and the creation of homozygous lines, including double haploids in plant breeding programs.

The term haploidt often appears as a variant spelling of haploid; the standard usage in biology is haploid.