In this article we will discuss about:- 1. Meaning of Gene Interactions 2. Characteristics of Gene Interaction 3. Gene Interaction for Comb Shape in Poultry.
Meaning of Gene Interactions:
When expression of one gene depends on the presence or absence of another gene in an individual, it is known as gene interaction. The interaction of genes at different loci that affect the same character is called epistasis.
The term epistasis was first used by Bateson in 1909 to describe two different genes which affect the same character, one of which masks the expression of other gene. The gene that masks another gene is called epistatic gene, and the gene whose expression is masked is termed as hypostatic gene. Epistasis is also referred to as inter-genic or inter-allelic gene interaction.
Characteristics of Gene Interaction:
The interaction of genes has several characteristics.
The important features of gene interaction are briefly described below:
i. Number of Genes:
The epistatic gene interaction always involves two or more genes. This is an essential feature of gene interaction.
ii. Affect same Character:
The epistatic genes always affect the expression of one and the same character of an individual.
iii. Expression:
The phenotypic expression of one gene usually depends on the presence or absence of epistatic gene. The gene which has masking effect is called epistatic gene and the gene whose effect is masked is known as hypostatic gene.
iv. Modification of Dihybrid Segregation Ratio:
Epistasis leads to the modification of normal dihybrid or tri-hybrid segregation ratio in F2 generation.
v. Genetic Control:
Epistasis is usually governed by dominant gene, but now cases of recessive epistasis are also known.
Gene Interaction for Comb Shape in Poultry:
In gene interaction, sometimes two dominant genes controlling the same character produce a new phenotype in F1 when they come together from two different parents. Such case of gene interaction was observed by Bateson and Punnett for comb shape in poultry.
There are three types of comb shape in poultry, viz., rose, pea and single. The comb shape is controlled by two pairs of alleles. The rose comb is governed by a dominant gene R and pea comb by a dominant gene P. The single comb is governed by two recessive genes (rrpp).
When a cross was made between rose (RRpp) and pea (rrPP), a new phenotype called walnut developed in F1. The walnut comb developed as a consequence of combining two dominant alleles R and P together in F1. Inter-mating of F1 birds produced four types of combs, viz., walnut, rose pea and single in 9 : 3 : 3 : 1 ratio in F2 generation.
Here individuals with R-P-(9/16) genotypes produce walnut comb, because two dominant genes together produce walnut comb. Individuals with R-pp (3/16) will give rise to rose comb, and those with rrP-(3/16) genotypes will produce pea comb. The single comb (1/16) will develop from a double recessive, genotype (Fig. 8.1).