Laws of inheritance G.Mendel for mono-hybrid crossings are also preserved in the case of a more complex dihybrid one. With this kind of interaction, the parent forms differ in two pairs of contrasting signs.
Let us consider a dihybrid crossing andconfirmation of G. Mendel's laws by example. Two varieties of peas were crossed: with white flowers and a normal aureole and with purple flowers and an elongated corolla. All individuals of the first generation had white flowers with a normal aureole. From this we conclude that the white color (denoted by C) and the normal length (we will write E) are dominant signs, while the purple color (c) and the elongated corolla (e) are recessive. When self-polluting plants of the first generation, splitting occurs. For better visibility, we will draw up a scheme for crossing.
The first crossing is: P1 CCEE x ssee
G 2Сс and 2Ее
F1 GCE
The second crossing (self-fertilization of F1 hybrids):P2 Cce x Cce. Dihybrid breeding occurs with the formation of 16 types of zygotes. Each gamete will contain 1 representative each from a pair of C-s and E-e genes. In this case, the gene C can be combined with equal probability with E or e. In turn, and c can combine with E or e. As a result, the hybrid CcEe forms with the same frequency 4 types of gametes: CE, Ce, cE, ce. Having lunch with each other, they form such organisms: 9 whites with a normal corolla, 3 whites with an elongated corolla, 3 purple with a normal corolla, and 1 purple with an elongated corolla.
In the second generation as a result of crossingIn addition to hybrids that look like parental forms, forms with a new combination of characters (combative or hereditary variability) are formed. This phenomenon plays an important role in evolution, gives new combinations of adaptive features. Also actively used in breeding, where the crossing of plants and animals of improved varieties and breeds makes it possible to breed new species.
The number of phenotypes in F2 is less than the number of genotypes. This is due to the fact that different combinations of gametes can give the same morphological features. So, we get a splitting by the phenotype - 9: 3: 3: 1.
All patterns of inheritance, whichestablished G. Mendel for mono- and di-hybrid crosses, are also characteristic for more complex combinations. Thus, polyhybrid hybridization occurs when the organisms taken for this purpose are distinguished by three or more contrasting features. At the heart of such a fusion of gametes and the redistribution of genetic information lie the laws of splitting and independent inheritance of characters.
From all the above, we conclude thatDihybrid interbreeding is, in fact, two independently walking simple crosses, where one alternative attribute (mono-hybrid) is taken into account. This is true for both plants and animals.
