What is a dihybrid crossing

The laws of G. Mendel's inheritance for mono-hybrid crossings are also preserved in the case of a more complex dihybrid. With this kind of interaction, the parent forms differ in the two pairs of contrast characteristics.

Let us consider the dihybrid hybridization and confirmation of G. Mendel's laws by the example. Two varieties of peas were crossed: with white flowers and a normal aureole and with purple flowers and an elongated corolla. All the 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 features, 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 hybrids F1): 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 crossing, in addition to hybrids that look similar to the parent forms, forms with a new combination of characteristics (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 derive 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.

Such a hybridization is possible if the dominant genes are located in non-homologous chromosomes. The cytological basis of this fusion and redistribution is meiosis and fertilization. G. Mendel noted that with this interaction of genes, each pair of characteristics is inherited independently of one another, freely combining in all possible combinations (independent inheritance).

All the inheritance patterns that G. Mendel established for mono- and dihybrid crossings are also characteristic of more complex combinations. Thus, polyhybrid interbreeding occurs when the organisms taken for this are distinguished by three or more contrasting features. At the basis of such a fusion of gametes and the redistribution of genetic information lie the laws of splitting and independent inheritance of characters.

From all of the above, we conclude that dihybrid crossing is, in fact, two independently running simple crossings, where one alternative attribute (mono-hybrid) is taken into account. This is true for both plants and animals.