Types of Intergenic Interaction

Inter-genic Interaction:

In gene interaction following observations and assumptions are found:
1. Genes that interact are present on different loci and are unlinked. These assort independently during gamete formation.

2. If complete dominance exists between the alleles of any gene pair or both the gene pairs, such as AA and Aa or BB and Bb have the same genetic effects, the representation A- or B- is used to represent both the combinations (AA or Aa). Therefore, the (-) indicates that either of the alleles may be present without influencing the phenotype.

3. All P1 crosses will involve homozygous individuals, AABB x aabb or AAbb x aaBB. Therefore, the F1 generation always has only the heterozygous genotype, AaBb.

4. The results of F2 generation are conclusive. With two pairs of genes F2 genotypic ratio is 9:3:3:1 = 16, A – B – = 9/16, A – bb = 3/16, aaB – = 3/16 and aabb = 1/16.

Types of Intergenic Interaction:

There are mainly two types of Intergenic Interaction:

    1. Dominant Epistasis

    2. Recessive Epistasis

Dominant Epistasis:

In dominant epistasis out of two pairs of genes the single dominant allele of one gene masks the activity of the other allelic pair (Bb). Since the dominant epistatic gene A exerts its epistatic influence by suppressing the expression of gene B or b, it is known as dominant epistasis.

Recessive Epistasis:

Epistasis due to a recessive gene is known as Recessive Epistasis, out of the two pairs of genes, the recessive epistasis gene masks the activity of the dominant gene of the other gene locus. The dominant A expresses itself only when the epistasis locus C also has the dominant gene if the epistasis locus has recessive gene c, gene A fails to express. It means both ccAA and ccaa individuals will have the same phenotype so that the over all phenotype becomes 9:3:4.