Term for the existence of different feature variants (alleles) at the same gene loci of homologous chromosomes. A feature under consideration comes twice with a double set of chromosomes and with that grapevine often in two different versions. Relative to the entirety of the varieties However, a certain characteristic can be present in up to 30 different variants, whereby only two of the possible alleles are realized at one gene location in a vine plant. In sexual reproduction, only one simple set of chromosomes is inherited per parent. At the Rebstock this is achieved by germinating a fertilized seed kernel of the berry into a plant. Chance decides which of the two homologous chromosomes of a parent is passed on in a 50:50 chance. Together with half the chromosome set of the second parent, the embryo again has a complete but newly mixed chromosome set with only half of the maternal alleles, but enriched by the new paternal alleles. This is also called mixed, split, unequal or unequal inheritance of the fertilized egg.
In the course of the life history of a vegetatively propagated variety, more occur mutations so that the cloned variety individuals in their allele combinations increasingly differ from the original type and from each other (variety clones, mutants, variants, game types ). These deviations are also passed on to the offspring. This phenomenon of polymorphism of the alleles within a sexually reproductive population with many different, possible alleles per locus is particularly pronounced in the vine. Therefore, in contrast to homozygous plants (e.g. cereals), there is an inability to produce descendants of the same type from seedlings. Heterozygosity causes the seedling not only from sexual reproduction of the original vine (mother vine) genotypisch deviates greatly, but also phenotypically is different. This is used in the new breed of grape varieties where other characteristics are desired in the offspring. This positive phenomenon is called heterosis, The production is genetically identical Clones (Duplicates) for duplication as it is in nurseries can only be practiced by vegetative propagation respectively. See also under DNA,