laws of inheritance Mendel for monohybrid cross preserved in the case of a more complex two-hybrid.In this type of interaction between parental forms differ in the two pairs of contrasting characteristics.
Consider the dihybrid cross and the confirmation of the laws of Mendel as an example.Crossed two varieties of peas: with white flowers and a normal rim and purple flowers and elongated rim.All the individuals of the first generation had a normal white flowers with a whisk.From this we conclude that the white color (call it C) and normal length (write E) - is a dominant trait and purple color (s) and an elongated whisk (e) - recessive.When the first generation of self-pollination of plants splits.For better clarity to chart crossing.
first mating: P1 x CCEE CCEE
G 2Ss and 2Ee
F1 CCEE
second mating (selfing hybrids F1): P2 x CCEE CCEE.Dihybrid cross is to produce 16 types of zygotes.Each gamete will contain one representative from each pair of genes, and a couple E's.This gene C is equally likely to be combined with E or e. In turn, and can combine with E or e. As a result, the hybrid forms CCEE with equal frequency 4 types of gametes: CE, Xie Xie Xie.Concatenate together, they form such organisms: 9 white with a normal rim, 3 white with an elongated rim, 3 purple with a normal rim and 1 with elongated purple rim.
second generation as a result of cross-breeding in addition to hybrids that resemble the parental forms, shapes are formed with a new combination of attributes (combinative, or genetic variation).This phenomenon plays an important role in the evolution provides new combinations of adaptive features.It is also actively used in breeding, where the crossing of plants and animals of improved varieties and breeds makes it possible to deduce new species.
number of phenotypes in F2 is less than the number of genotypes.This is due to the fact that the union of different gametes can give the same morphological characteristics.Thus, we obtain cleavage phenotype - 9: 3: 3: 1.Such
dihybrid cross possible if dominant genes are located in chromosomes nonhomologous.Cytological basis of such a merger and re - meiosis and fertilization.Mendel observed that when such an interaction of genes, each pair of traits inherited independently of each other, freely being combined in all possible combinations (independent inheritance).
All patterns of inheritance that Mendel set to mono- and dihybrid cross, typical for a more complex combinations.For poligibridnoe interbreeding occurs when taken for that organisms differ in three or more contrasting features.At the heart of such a merger of gametes and redistribution of genetic information on the laws and splitting the independent inheritance of characters.
From the foregoing, we conclude that dihybrid cross - is, in fact, two independently reaching simple crossing, which takes into account one alternative feature (monohybrid).This is true for plants and animals.
