Ploidy
Ploidy is a term from genetics and cell biology. It is used to indicate the number of chromosome sets in a cell. Most eukaryotes have either one set (called haploid) or two sets (called diploid). Some other organisms are polyploid, they have more than two sets of chromosomes. Some amphibians (and the endosperm cells of plants) are triploid, with 3 sets. Some kinds of trouts or salmons have 4 sets (tetraploid). Other examples:
- wheat: 6 sets (hectaploid)
- certain sturgeons: 8 sets (octoploid)
- strawberries: 8 sets (octoploid)
- plumed cockscomb (a plant, Celosia argentea): 12 sets (dodecaploid)
- Bryophytes: body has one set; sporophyte has two sets.
Sex cells (gametes) are almost always haploid. If the reproductive stage (adult) is polyploid, then the gametes will have half the ploidy number of chromosomes.
There are some variations of ploidy which are not discussed here. Some plant species with certain types of polyploidy do not use sexual reproduction, but survive with asexual methods.
