Genotype as an integral system

The interaction of genes is the joint action of several genes, as a result of which a trait appears that the parents do not have, or the manifestation of an existing trait is enhanced.
To explain the results of gene interaction, it is important to understand the mechanism of trait formation.

A gene is a piece of DNA that encodes information about a single protein. In the simplest case, the formation of a trait can occur as a result of the action of one protein, the synthesis of which is determined by one gene

– but usually the trait is formed as a result of complex biochemical processes. In the cell, there is an interaction between enzyme proteins, the synthesis of which is determined by genes, or between substances that are formed under the influence of these enzymes.

The following types of manifestation of genes in the phenotype are possible:

one trait is formed as a result of the interaction of several proteins, the synthesis of which is determined by several genes

one gene determines protein synthesis, which affects the formation of several traits

– as shown in the diagram.

Interaction is possible both between allelic genes and between non-allelic genes.

Allelic genes are located in the same regions of homologous chromosomes and determine one trait. Examples of the interaction of allelic genes:

• complete domination;
• incomplete dominance.

(For information on the interaction of allelic genes, see the previous subtopics.)

Non-allelic genes are located in different regions of non-homologous chromosomes. Forms of interaction of non-allelic genes:

• complementarity;
• epistasis;
• polymerism.

Complementarity, epistasis, and polymeria are interactions in which multiple genes define one trait.

Inheritance, in which one gene affects the formation of several traits, is called pleiotropy (or multiple gene action).