noun, plural: polyploids
Ploidy pertains to the number of sets of homologous chromosomes that make up the genome of an organism or a cell. The set of chromosomes is designated as n. There are different ploidy levels based on the number of sets. A single set of chromosomes is described as monoploid (1n) whereas two sets of (homologous) chromosomes are referred to as diploid (2n). The somatic cells of humans are diploid. This means that the genome is made up of two sets of homologous chromosomes where each set originated from the parents. The two sets are derived from the chromosomes from the union of female and male gametes. The chromosomes of the resulting offspring would be homologous since the chromosomes from the female gamete would have the corresponding chromosomes from the male gamete based on the likeness of morphology and linear sequence of gene loci. Having multiple sets, i.e. more than two, of these homologous chromosomes is described as polyploid. A cell or an organism having three sets of homologous chromosomes (3n) is described as triploid. Having four sets of homologous chromosomes (4n) describes a tetraploid cell or organism. Extremely large number of sets may be designated by number (for example 15-ploid for fifteen sets). Polyploidy is common in plants.
Word origin: poly- (many) + ploidy