A complete haploid chromosome set. The term is used in discussions of * polyploidy. A diploid organism contains two homologous genomes unless it is an interspecific hybrid, in which case it contains two different genomes. An autopolyploid contains three or more homologous genomes while an allopolyploid has two or more pairs of different genomes. The number of chromosomes in a genome (termed the base or basic number) is usually between six and thirteen and is represented by the symbol x. In diploid organisms the number of chromosomes in the genome is equivalent to the haploid number n, and so 2n = 2x. However in tetraploid organisms 2n = 4x, in hexaploid organisms 2n = 6x, etc. For example, al-lohexaploid wheat, Triticum aestivum, contains six genomes designated AA, BB, and DD each of which contains seven chromosomes, i.e. x = 7. Thus n — 3x = 21 and 2n = 6x = 42. |
