Designation for the existence of different feature variants (alleles) at the same loci of homologous chromosomes. A considered feature comes twice in a double set of chromosomes and in the grapevine often in two different variants. Relative to the totality of varieties However, a particular feature may be present in up to 30 different variants, wherein in a vine each only two of the possible alleles are realized at a Genort. In sexual reproduction, only one single set of chromosomes per parent is inherited. At the Rebstock This is realized by the germination of a fertilized seed of the berry to a plant. Which of the two homologous chromosomes of a parent is passed on is decided by chance in a 50:50 chance. Together with half of the set of second-parent chromosomes, the embryo has a complete, yet remixed set of chromosomes 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 life history of a vegetatively propagated variety more occur mutations so that the cloned variety individuals in their allele combinations increasingly deviate from the original type and from each other (variety clones, mutants, variants, game types ). These deviations are also inherited to the offspring. This phenomenon of polymorphism of the alleles within a sexually reproducing population with many different possible alleles per locus is particularly pronounced in the vine. Therefore, in contrast to homozygous plants (for example cereals) there is the inability to produce seedlings of the same origin. The heterozygosity causes the seedling from sexual reproduction of the original vine (mother vine) not only genotypisch strongly deviates, but also phenotypically is different. This is useful for the new breed of grape varieties where other characteristics are desired in the offspring. This positive phenomenon is called heterosis, The production of genetically identical Clones (Duplicates) for duplication, as it is in nurseries can be practiced only by vegetative propagation respectively. See also below DNA,