Information AboutPolyploidy |
| CATEGORIES ABOUT POLYPLOIDY | |
| classical genetics | |
| speciation | |
| SHOPPER'S DELIGHT | |
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EXAMPLES Polyploidy occurs in some Animal s, such as Goldfish , salmon, and salamanders, but is especially common among Fern s and flowering Plant s, including both wild and cultivated Species . 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. Many agriculturally important plants of the genus '' Brassica '' are also tetraploids; their relationship is described by the Triangle Of U . Examples in animals are more common in the ‘lower’ forms such as flatworms, leeches, and brine shrimp. Reproduction is often by Parthenogenesis since polyploid animals are often sterile. Polyploid salamanders and lizards are also quite common and parthenogenetic. While mammalian liver cells are polyploid, rare instances of polyploid Mammals are known, but most often result in Prenatal death. Presently, the only known exception to this rule is an Octodontid Rodent of Argentina 's harsh Desert regions known as the Red Viscacha-Rat (''Tympanoctomys barrerae'') (not really a Rat at all, but kin to Guinea Pig s and Chinchilla s), whose "new" diploid {Link without Title} number is 102 and whose cells are roughly twice normal size as a result. Its closest living relation is ''Octomys mimax'', the Andean Viscacha-Rat of the same family, whose 2n=56. It is surmised that an ''Octomys''-like ancestor produced tetraploid (i.e., 4n=112) offspring that were, by virtue of their doubled chromosomes, reproductively isolated from their parents; but that these likely survived the ordinarily catastrophic effects of polyploidy in mammals by shedding (via Translocation or some similar mechanism) the "extra" set of Sex Chromosomes gained at this doubling. Polyploidy can be induced in cell culture by some chemicals: the best known is Colchicine , which can result in chromosome doubling, though its use may have other less obvious consequences as well. In plant breeding, the induction of polyploids is a common technique to overcome the sterility of a hybrid species. Triticale is the hybrid of Wheat (''Triticum turgidum'') and Rye (''Secale cereale''). It combines sought-after characteristics of the parents, but the initial hybrids are sterile. After polyploidization, the hybrid becomes fertile and can thus be further propagated to become triticale. Salsify or "goatsbeard" is another example of polyploidy resulting in new species. POLYPLOID CROPS Polyploid plants in general are more robust and more sturdy than diploids. In the breeding of crops, those plants that are stronger and tougher are selected. Thus many crops have unintentionally been bred to a higher level of ploidy:
Some crops are found in a variety of ploidy. Apples , Tulips and Lilies for example are commonly found as both diploid and triploid. TERMINOLOGY Autopolyploidy Autopolyploids are polyploids with chromosomes derived from a single species. Autopolyploids can arise from a naturally occurring spontaneous genome doubling (for example potato). Banana s and Apple s can be found as triploid autopolyploids. Allopolyploidy Allopolyploids are polyploids with chromosomes derived from different species. Triticale is an example of an allopolyploid, having six chromosome sets, four from wheat (Triticum turgidum) and two from rye (Secale cereale). Cabbage is a very interesting example of a fertile allotetraploid crop (see Triangle Of U ). Amphidiploidy is another word for an allopolyploid. The giant Tree '' Sequoia Sempervirens '' or Coast Redwood has a hexaploid (6n) genome, and is also thought to be autoallopolyploid (AAAABB). Paleopolyploidy Ancient genome duplications probably characterize all life. Duplication events that occurred long ago in the history of various Evolutionary Lineages can be difficult to detect because of subsequent diploidization (such that a polyploid starts to behave cytogentically as a diploid over time) as mutations and gene translations gradually make one copy of each chromosome unlike its other copy. In many cases, these events can be inferred only through comparing Sequenced Genomes . Examples of unexpected but recently confirmed ancient genome duplications include the baker's Yeast ('' Saccharomyces Cerevisiae ''), mustard weed/thale cress ('' Arabidopsis Thaliana ''), Rice ('' Oryza Sativa ''), and an early Evolution ary Ancestor of the Vertebrates (which includes the Human lineage) and another near the origin of the Teleost Fishes . Angiosperms ( Flowering Plants ) may have paleopolyploidy in their ancestry. All Eukaryote s probably have experienced a polyploidy event at some point in their evolutionary history. REFERENCES
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