Haploid

A haploid cell has one set of chromosomes, with one copy of each chromosome type. In organisms with sexual reproduction, gametes are commonly haploid.

Ploidy: The number of complete chromosome sets in a cell or organism. Haploid names the ploidy level with one chromosome set.
Gamete: A reproductive cell that fuses with another cell during sexual reproduction. Eggs and sperm are haploid in many animals.
Meiosis I: The first meiotic division, which separates homologous chromosomes into different cells. Separating homologs halves the chromosome-set number.
Saccharomyces cerevisiae: A budding yeast species that can grow as either haploid or diploid cells. Its two mating types make haploid growth and mating experimentally accessible.
Chromosome: A DNA molecule packaged with proteins that carries genetic information. A haploid set contains one of each chromosome type.
Zygote: The first cell formed when two gametes fuse. A zygote usually begins development with two chromosome sets, one from each haploid gamete.
Meiosis II: The second meiotic division, which separates sister chromatids. It distributes chromatids among cells that already have one chromosome set.
Chlamydomonas reinhardtii: A unicellular green alga commonly used in research on photosynthesis and cell biology. Its vegetative stage is haploid, with diploidy limited to the zygote.
Homologous chromosome: One of a matching pair of chromosomes that carry the same genes at corresponding locations. Haploid cells have one homolog from each pair found in diploid cells.
Alternation of generations: A life cycle in which multicellular haploid and diploid stages alternate. Plants and some algae include a multicellular haploid generation.

Linked from 24 pages