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chimera

chimera (GB)
quimerismo (ES)
chimère (F)
chimaera (N)
chimera (I)
quimerismo (PO)

Name for an organism whose cells are derived from at least two genetically distinct zygotic lines (diploid cells). In botany, this is used for those plants whose plant body has mutated cell lines in different tissues or organs. The relatively common phenomenon is known from ornamental plants, where sectoral chimeras occur with multicolored petals or oblong striped, white-green or purple-green-white foliage leaves. Periclinic chimeras are plants whose external epidermis tissue is affected by mutational events of the genotype the internal cell lines deviates, the mutations occur independently in both cell lines and at different loci. Due to the double set of chromosomes of the vine, a gene locus can mutate into four different alleles.

Especially with old, widespread and many vegetative somatic chimeras are the normal case for duplicated varieties, since the two basic cell lines L1 (epidermis cells) and L2 (inner cells) were already spatially separated from each other with the differentiation of the embryo in the seed and thus mutated independently for centuries. For ancient varieties like Pinot and Traminer (see in detail) mutations have led to the formation of numerous somatic chimeras that can differ genotypically from one, several or all four possible alleles of a locus. These are also referred to as shoot or bud mutations, because from the buds by cell division of the mutated stem cells a whole new shoot with the changed or new somatic and thus visible properties grows.

In the case of the vine, a periclinic mutation in the epidermis line L1 can be manifested, for example, by a stronger hairiness than in the two varieties Pinot Meunier (Black Riesling) or Lladoner Pelut, There are also so called mericlinic chimeras like the Pinot gris, on whose gray grapes fruit branches with white berries can occur. The Tressot Panaché is a classic sectoral chimera with white and blue sectors on the skin of individual berries that appear either white, blue, or white-blue-striped in sectors. However, most mutational events are not or only gradually visible externally. It may, for example, be a slight shortening of the ripening period, a darker berry color or a more intense taste. For fixing such Klonmutante The vegetative propagation of the mutated axillary drive belongs to an independent and further propagated vine. Most clones of the Pinot Noir have been shown to be more accurate than periclinic chimeras, which was to be expected because it is extremely unlikely that a spontaneous mutation event would occur in both cell lines at the same site DNA strand occurs.

In such genotypically characterized and distinguishable clonal variants, one should speak better of cloning mutants, because a clone in the strict sense is initially only a copy of the original, which develops only by mutations to a differentiable clone in viticultural sense. That I adventitious and water shoots develop only from the cell lines of the L2 layer, somatic chimeras can change without additional mutational events, solely by vegetative propagation from adventitious sprouts. The resulting plants then have only the mutation history of the L2 cell line. In summary, one can say that a chimera always results from a mutation. However, not every mutation can be called a chimera, although this is the rule for the vine. Also a refined Vine is a chimera, in this case a mesoclinic chimera (upper and lower region). See also on this topic molecular Genetics,

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