euploid diploid A ploidy quality inhering in a bearer by virtue of the bearer's having two copies (homologs) of each chromosome, usually one from the mother and one from the father. PATO:0001394 The exact number may be one or two different from the 2n number and still be classified as diploidy (although with aneuploidy). Nearly all mammals are diploid organisms, although all individuals have some small fraction of cells that are polyploidy.