hexaploid

Hexaploid describes an organism that carries six complete sets of chromosomes. In this context, the chromosome count is 2n = 6x, where x is the base chromosome number of the species. Hexaploidy is a form of polyploidy and is far more common in plants than in animals, arising by genome duplication, hybridization between species, or both.

Hexaploidy can originate as autopolyploidy, from doubling of a single genome, or as allopolyploidy, from the combination of distinct genomes from related species followed by chromosome doubling. Allopolyploids often stabilize with several subgenomes that behave as separate chromosome sets. A well-known example is bread wheat, Triticum aestivum, an allohexaploid with genomes designated AABBDD and a total of 42 chromosomes (2n = 6x = 42). It is derived from hybridization among three diploid progenitors representing the A, B, and D genomes, followed by chromosome doubling.

Cytogenetically, meiosis in hexaploids typically favors pairing between homologous chromosomes within each subgenome, rather than between subgenomes. In bread wheat, genetic mechanisms such as the Ph1 locus reduce homoeologous pairing, promoting regular segregation and fertility.

In agriculture and evolution, hexaploidy can confer advantages such as increased cell and organ size, greater genetic redundancy, and enhanced adaptability. Breeding hexaploids presents challenges due to complex inheritance and potential chromosomal rearrangements, but it also opens avenues for trait diversification. Detection and study of hexaploids rely on chromosome counting, flow cytometry, and molecular-genetic approaches to understand genome organization and stability.