-ploid Also -ploidy.
The number of sets of chromosomes in a cell.
[From haploid and diploid (see text).]
The two oldest forms are haploid (Greek haploos, single), of a cell or nucleus that has a single set of unpaired chromosomes, and diploid (Greek diplous, double), containing two complete sets of chromosomes, one from each parent. They were formed using the ending -oid, but the last two letters of the Greek stems became attached to it to make a new ending.
Other examples are triploid, containing three homologous sets of chromosomes; tetraploid, containing four; hexaploid, containing six; polyploid, containing more than two homologous sets of chromosomes; aneuploid (Greek an-, not, plus eu-, well, good), having an uneven number of chromosomes.
The state of having such chromosome arrangements is expressed by -ploidy: aneuploidy, polyploidy, triploidy.