Non allelic gene interaction; Introdution Definition of Epistasis Dominant and recessive epistasis with Examples

2. These kinds of genetic interactions between the alleles of a single gene are referred to as allelic or intra-
allelic interactions.
Non-allelic or inter-allelic interactions also occur where the development of single character is due to two
or more genes affecting the expression of each other in various ways.
What is allelic and non allelic interaction?
Definition:
Epistasis can be defined as a gene interaction whereby one gene interferes with the phenotypic expression of
another non allelic gene or genes.
The gene or locus which suppresses or masks the action of a gene at another locus is called epistatic gene. The gene
or locus whose expression is suppressed by an epistatic gene is called hypostatic gene

3. Types of Epistasis
Epistasis is of different types namely dominant, recessive and dominant
recessive.
Dominant epistasis: A dominant epistastic suppresses the expression of a non allelic gene (dominant or recessive).
F2 phenotypic ratio: 12:3:1
Example: In summer squash fruit colour may be white, yellow or green. White fruits are produced by a domain
epistatic allele ‘W’. At another locus ‘Y’ for yellow fruits is dominant to its allele ‘y’ for green fruits. Dominant white
hides the effect of yellow or green. A consequence of this dominant epistasis is that the hybrid ratio

4. Recessive epistasis: A recessive epistastic gene suppresses the expression of a non allelic gene only when the
former is in homozygous recessive state.
F2 phenotypic ratio: 9:3:4 Example: A black Labrador homozygous for the dominant alleles (BBEE) is crossed with a
yellow Labrador homozygous for the recessive alleles (bbee).
On intercrossing the F1, the F2 progeny was obtained in the following ratio : 9 black : 3 brown: 4 yellow.