chromosomedoubling

Chromosome doubling, also referred to as whole-genome duplication or polyploidization, is the process by which a cell or organism gains an extra complete set of chromosomes, increasing its chromosome number beyond the diploid condition. It is distinguished from aneuploidy, where individual chromosomes are gained or lost.

Mechanisms include endoreduplication (or endoreplication), in which the genome is replicated without mitosis, producing 4n, 8n, or higher levels within a single nucleus. Cytokinesis failure during mitosis can yield multinucleate or mononucleate polyploid cells. Unreduced gametes can fuse during sexual reproduction to form autopolyploid offspring, while hybridization between species followed by chromosome doubling can produce allopolyploids.

Biological implications vary by lineage. In plants, polyploidy is common and often linked to increased cell and organ size, vigor, and the potential for speciation; many crops are polyploid, such as bread wheat, which is allohexaploid. In animals, polyploidy is less frequent and can present developmental challenges, though certain tissues (for example, liver) can naturally become polyploid. In cancer, whole-genome doubling events are observed and can contribute to chromosomal instability and tumor evolution.

Detection and study typically involve flow cytometry to estimate DNA content, karyotyping to count chromosomes, and molecular methods such as fluorescent in situ hybridization, comparative genomic hybridization, or sequencing-based copy-number analysis.

Terminology and related concepts include endopolyploidy, which refers to tissue-specific polyploidy within an organism, and the distinction between polyploidy and aneuploidy, where chromosome number is not an exact multiple of the haploid set.