polyploid

[duō bèi tǐ]

Individuals with three or more genomes in somatic cells

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Polyploid: English name: polyploid somatic cell Contains three or more Chromosome Individuals. Polyploid in Biosphere Widely existing, common in higher plant Due to different origins of genome, it can be divided into Autopolyploid and Allopolyploid 。

Chinese name: polyploid
Foreign name: polyploid
Concept: Three or more somatic cells Chromosome individual

Exists in: Widely existing in the biological world
Divided into: Autopolyploid and Allopolyploid
Common in: higher plant in

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This is speciation The other way is that it can be produced only after one or two generations New species The way. Once polyploid organism is formed species It happens Reproductive isolation , so it has become a new species, so this way is called explosive. Polyploid in Animal kingdom It is rare, but quite common in the plant world. Many plant species are produced through polyploid pathway. About 33% of the species are polyploid. angiosperm More than 40% of them are polyploids. Wheat 、 oats , cotton, tobacco, sugarcane Banana 、 Apple , pears, daffodils, etc Polyploidy Of. Banana, some potato varieties are triploid Of. Generally, potatoes are tetraploid 。 Fern Many are polyploids, Gymnosperms Less polyploid, but famous redwood （ Sequoia sempervirens ）Is Hexaploid 。

Formation mode

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There are two ways to form polyploid. One is that after chromosome replication due to some unknown reason, the cell does not divide, resulting in doubling of chromosomes in the cell, thus forming Autopolyploid （autopolyploid）； The other is polyploid produced by hybridization of different species, called Allopolyploid （allopolyploid）。

Autopolyploid is relatively rare. At the beginning of the 20th century, Netherlands Geneticists study a scabish According to the heredity of Oenothera corckiana, the chromosome of one evening primrose has doubled from 24 (2n) to 48 (4n) tetraploid Botany. This tetraploid plant is produced by crossing with the original diploid plant triploid Plants are sterile（ Meiosis Chromosome mismatch). So this tetraploid plant is a new species. Hugo de Vries named this new species Oenothe.

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The general characteristics of polyploid plants are thick stems, large leaves, large flowers and large fruits, but they often grow slowly, stunt and mature later.^[1] Polyploid plant sugars and protein etc. Nutrients The content of. For example, tetraploid Grape Its fruit is much larger than that of diploid grape, tetraploid grape tomato Of vitamin C Of Content ratio The number of diploid varieties has almost doubled.^[2]

Artificial polyploid

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Through experiments, we can artificially cultivate Autopolyploid plant , for example, watermelon yes diploid , with 11 pairs (22) of chromosomes (2n=22). In watermelon seedling Period Colchicine Treating the growth tip of seedlings, destroying the dividing cells Spindle And doubled the number of chromosomes in the cell, thus obtaining watermelon plants with quadruple chromosomes (4n). tetraploid Watermelon can bear fruit and produce seeds, which can be cultivated into tetraploid watermelon lines. If tetraploid watermelon accepts diploid watermelon pollen , the offspring are triploid 。 Because this triploid Meiosis Chromosomes can not be linked and paired normally and can not produce normal gamete There is no normal seed in triploid watermelon fruit. Marketable Seedless watermelon This is the triploid watermelon.

Allopolyploid There are many examples. cultivate Wheat (Triticum vulgaris) originated in this way. About 6000 years ago, one species had 14 chromosomes（ diploid ）Of wild wheat, called A grain of wheat (Triticum monococcum), and a weed Aegilops (Aegilops sp.). The normal diploid of this weed is also 14 chromosomes, but they are different from the 14 chromosomes of a grain of wheat (different origins), so they cannot pair, so Hybrid offspring It is sterile. However, due to the low temperature, the hybrid offspring suddenly Chromosome doubling , forming a Allopolyploid , i.e. two Wheat （Triticum dicoccoides）。 emmer wheat It has 28 chromosomes, or 14 pairs of chromosomes. Two grain wheat crosses with another diploid Aegilops squarrosa. Two grain wheat has 28 chromosomes, and Aegilops squarrosa has only 14 chromosomes. The hybrid offspring are sterile. Because of the low temperature, this Hybrid The chromosomes of wheat were suddenly doubled, forming an allopolyploid with 42 (28+14) chromosomes, namely cultivated common wheat.

Because hybrids produced by hybridization of different species of plants are often highly sterile, chromosome doubling is necessary to breed allopolyploid plants in order to produce offspring capable of fruiting and reproduction. For example, set Asian cotton (2n=26) and wild American cotton (2n=26) The hybrid obtained by hybridization is doubled by chromosome（ Colchicine Processing) get Chromosome number Is 4n=52 cotton plant, and Cultivated species American cotton is the same. Similar tests were conducted in Wheat 、 Brassica 、 Plum , tobacco and other plants are successful, providing a strong basis for the origin of species. In these cases, genetic relationship Between distant species Hybrid offspring Fertility One of the reasons is that the chromosome composition of hybrids comes from different species of plants Meiosis Middle chromosomes cannot pair. After chromosome doubling, the problem of pairing was solved and the fertility was improved.

Polyploid Studies in China

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Chinese Agriculture Scientists Triticale Same Allopolyploid New species. Wheat has 42 chromosomes (6n=42), Rye There are 14 chromosomes (2n=14). Wheat Hybridization with rye produces hybrids with 21+7 chromosomes. Because chromosomes cannot pair, Hybrid sterility 。 But with Colchicine Treatment, doubling the number of chromosomes (42+14), thus becoming a fertile alien Octoploid The triticale has been newly planted.

About polyploidy: artificially obtained polyploids often have sterile characteristics, such as Autotetraploid Its own fertility and the fertility of crossing with diploid are very low. It is a very complicated and long process to select lines with good fertility and good seed bearing ability So Polyploid breeding It's easy to say, but not easy to operate It will take decades or even decades of work to breed a valuable variety

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