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 are triploid, with three sets. The endosperm cells in the seeds of many plants are also triploid. Some kinds of trout or salmon have four 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.