Allopolyploïdy

Allopolyploidy is a type of polyploidy where an individual contains sets of chromosomes from two or more different species. This contrasts with autopolyploidy, where the extra chromosome sets originate from the same species. Allopolyploidy typically arises from hybridization between two different species, followed by a doubling of the chromosome number. This doubling is crucial as it restores fertility to the hybrid, which would otherwise be sterile due to mismatched chromosomes during meiosis.

The process can be visualized as two parent species, say species A with chromosome set AA and species B with chromosome set BB, producing a hybrid with chromosome set AB. This AB hybrid is usually infertile because the chromosomes from A and B cannot pair properly during meiosis. If, however, the chromosome number doubles, the hybrid becomes AABB. Now, the A chromosomes can pair with each other, and the B chromosomes can pair with each other, allowing for the production of viable gametes and thus fertile offspring.

Allopolyploidy has played a significant role in plant evolution and is a major mechanism for speciation. Many important crops, such as wheat, cotton, and tobacco, are allopolyploids. The combination of genetic material from different species can lead to novel traits and increased adaptability. In some cases, the allopolyploid species may exhibit characteristics that are intermediate between the parent species, or entirely new traits not present in either parent. This genetic novelty is a key factor in the evolutionary success of allopolyploid organisms.