Ploidy refers to the number of sets of homologous chromosomes in the genome of a cell or an organism. Each set is designated by n. Thus, the term haploidy would refer to a state of being haploid, that is having half of the set of the homologous chromosomes relative to that in somatic cells. In humans and many other living things, the somatic cell contains two copies of genes. As such, they are referred to as diploid. Gametogenesis, the process of producing gametes, ends up with sex cells that are haploid. That is, the number of chromosomes is halved. This is essential so that during the union of gametes the resulting zygote would have a diploid state and thus the integrity of chromosomal number throughout generations is eventually preserved. In humans, for instance, the germ cell (a sperm or an egg cell) is haploid, which means it contains only one of each of the 23 chromosomes of the human genome, or it only has half the diploid (2n) number of a human somatic cell (which is 46).
Word origin: from Greek diplous, double
- haploid (adjective and noun)