GENE INTERACTION

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GENE INTERACTION

Definition:-

The phenomenon of two or more genes affecting the expression of each other in various ways in the development of a single character of an organism is known as gene interaction.

Most of the characters of living organisms are controlled/influence/governed by a collaboration of several different genes. Mendel and other workers assumed that characters are governed by single genes but later it was discovered that many characters are governed by two or more genes.

Types of Gene Interactions

Gene interaction can be classified as:-

01   Allelic/non-epistatic gene interaction: This type of interaction gives the classical ratio of 3:1 or 9:3:3:1.

02   Non-allelic/epistatic gene interaction:  In this type of gene interaction of genes located on same or different chromosomes interact with each other for their expression. Discovery of non-allelic gene interaction has been made after Mendel and can be understood by studying phenotypic trait or gene.

Gene interaction can be of following types.

Complementary Gene Interaction

1.            Involves of two pair of non-allelic genes.

2.         When dominant forms of both the genes involved in complementary gene interaction         are alone have same phenotypic expression 

        But, if they are present in combination, yield different phenotypic effect.

4.         Flower color in garden pea follows this type of gene interaction.

We have considered garden pea for the explanation of this type of gene interaction, in which it was noted for the first time. Two different varieties of garden pea produce same color flowers-whit. But on crossing they yield purple color flowers. Again in F2, 9 purple: 7 white segregation was observed.

Supplementary Gene Interaction

 

1.                 Involves two pair of non-allelic genes.

2.                 Affect the same character.

3.             One of the dominant genes has visible effect itself.

4.      Second dominant genes expresses itself when supplemented by the other dominant         genes of a pair.

5.         Coat color (black, albino and agouti) of mice flowers supplementary gene interaction.

In mice, black coat color is monogenitically dominant over albino and agouti. The offspring resulting from the cross between black and albino has agouti coat color.

            F2 generation shows segregation in the ratio 9 agouti: 3 black: 4 albino. This behavior is based on ratio of dihybrid cross, so the trait must be governed by two pairs of genes.

            Suppose, gene C is essential for the development of black coat color, so present in black mice and absent in albino mice. Albino mice contains only gene A, so produce albino phenotype.

            But, when gene A is present along with gene C, produces agouti phenotype. Both the gene in recessive form produce albino phenotype.

            So the cross will be as follows:

Cross between	F1	F2
CCaa X ccAAblack X albino	CcAa agouti	9 agouti : 3black : 4 albino

 Incomplete Dominance

 

Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele. This results in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles. Unlike complete dominance inheritance, one allele does not dominate or mask the other.

            Incomplete dominance occurs in the polygenic inheritance of traits such as eye color and skin color.

            Discovery if no allelic gene interaction has been made after Mendel and can be understood by studying phenotypic trait of gen.