Intermediate (genetics)
In genetics, an intermediate (from Latin intermedius , `` in between '') is a type of inheritance in which an intermediate hybrid form is formed in the external appearance ( phenotypic ) if two different variants ( alleles ) of the same in the genetic material ( genotypic ) Genes for different expressions of a trait exist ( heterozygosity ).
(1) Parent generation with pure inheritance systems (w / w or r / r).
(2) F 1 generation: All individuals look the same, the “ red ” and “white” genes result in a pink flower color.
(3) F 2 generation: Red , pink and white flower colors occur in a 1: 2: 1 ratio.
Most animals and plants have a double ( diploid ) set of chromosomes , each made up of a maternal and a paternal part. Therefore, there can be two variants (a, b) for a gene that differ from one another (heterozygous). If these alleles are identical in the genotype (homozygous), a characteristic appears in the phenotype either (a, a) with one ( A ) or (b, b) with the other ( B ) expression. With regard to the characteristics of the heterozygous genotype (a, b), a distinction can then be made between several forms of inheritance:
In the case of dominant-recessive inheritance, only the feature ( A ) appears on the part of the dominant allele (a), that on the part of the recessive allele does not.
In the case of codominant inheritance, both alleles develop the characteristics ( A and B ) in the phenotype independently of one another.
In the case of intermediate inheritance, on the other hand, there is a mixed characteristic expression, which is influenced by both alleles.
For example, a plant with genetic information for both red and white flowers shows pink flowers with intermediate inheritance. If only one of the two alleles carries information for a specific protein that is required for the formation of the flower pigment, the concentration of colorants in the flower is usually lower than in an individual with a homozygous genotype for this. The example of the magic flower ( Mirabilis jalapa ) described Carl Correns in 1909 a similar context, and also showed the leaf pigment , the concept of maternal or on the inheritance pattern of staining (green, white, variegated) cytoplasmic inheritance on.