Polyploidy

Polyploidy is a condition in which the cells of an organism have more than two paired (homologous) sets of chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes—one set inherited from each parent. However, polyploidy is found in some organisms and is especially common in plants. In addition, polyploidy occurs in some tissues of animals that are otherwise diploid, such as human muscle tissues. This is known as endopolyploidy. Polyploid cells and organisms are produced by various mechanisms, including abnormal cell division (mitosis or meiosis) and fusion of organisms.

File:Haploid, diploid ,triploid and tetraploid.svg

Haploid, diploid ,triploid and tetraploid

Types of Polyploidy

There are three types of polyploidy that can lead to reproductive isolation of an individual in the polyploid state. They are as follows:

• Autopolyploidy: Polyploidy resulting from duplication of one or more of an organism's chromosome sets. Autopolyploids are derived from a single species and have therefore identical sets of chromosomes. If the original species was diploid, the autopolyploid is a tetraploid.

• Allopolyploidy: Polyploidy resulting from the combining of the chromosomes of two different species. As a result, an allopolyploid can have more than two sets of chromosomes, each derived from a different species.

• Segmental allopolyploidy: Polyploidy resulting from the combining of the chromosomes of two different species, but with subsequent genetic recombination.

Polyploidy in Plants

Polyploidy is pervasive in plants and some estimates suggest that 30–80% of living plant species are polyploid, and many lineages show evidence of ancient polyploidy (paleopolyploidy) in their genomes. Significant examples of polyploidy exist in the plant kingdom. Wheat, for example, after millennia of hybridization and modification by humans, has strains that are diploid (two sets of chromosomes), tetraploid (four sets of chromosomes) with the common name of durum or macaroni wheat, and hexaploid (six sets of chromosomes) with the common name of bread wheat.

Polyploidy in Animals

Polyploidy is much less common in animals than in plants. It is most common in the amphibian and fish classes, but it can also be found in reptiles and mammals.

See Also

• Endopolyploidy
• Eukaryote
• Mitosis
• Meiosis
• Wheat

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