monoploidy

Monoploidy refers to organisms or cells that contain only a single complete set of chromosomes. In most eukaryotic organisms the normal cell cycle produces diploid cells that have two homologous copies of each chromosome, one inherited from each parent. A monoploid cell has only one copy of each chromosome and therefore lacks a homologous partner for many genetic processes.

Monoploid genomes can arise naturally or be produced intentionally. In many plant species, spontaneous monoploid individuals appear due to chromosome loss events, and they are often sterile or exhibit reduced fertility because meiotic pairing is impaired. In the laboratory, monoploid yeast and other model organisms are generated by eliminating one copy of the genome or by using haploid strains for genetic studies. Many bacterial species are naturally monoploid, with a single chromosome that serves as their entire genetic complement.

The study of monoploidy has practical applications. Haploid cells allow easier genetic manipulation because each phenotype directly reflects the genotype without dominance masking. In crop breeding, monoploid lines can be used as starting material for creating new combinations of traits through polyploidization. In biotechnology, monoploid microorganisms are valued for stable production of recombinant proteins or metabolites because their genetic makeup is simpler and less prone to recombination events that can alter production.

Monoploidy contrasts with aneuploidy, which involves abnormal numbers of chromosomes, and with diploidy, the typical state for many organisms. While monoploidy can confine genetic diversity, it can also streamline genetic analyses and have benefits in industrial strains where genetic stability and predictable behavior are desired.