AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

EPISTASIS

• When an allele of one gene masks expression of alleles of another gene and expresses its own phenotype instead, it is known as Epistasis.
• This is a Greek word meaning standing upon.
• The gene responsible for the suppression is called Epistatic and the genes, which are being suppressed, are called Hypostatic.

Types of Genetic Interaction in Dihybrid Ratio

GENETIC EXPLANATION	F2 PHENOTYPIC RATIO
	AABB		AABb	AaBB	AaBb	AAbb	Aabb	aaBB	aaBb	aabb
Classical Dihybrid Ratio	9					3		3		1
Complete dominance at one locus and Incomplete dominance at another locus (co-dominance)	3			6		1	2	3		1
Complete dominance lacking at either locus (co-dominance at both locus)	1		2	2	4	1	2	1	2	1
Complete dominance at one locus and Homozygous dominant lethal at another locus			6			3			2	1
Incomplete dominance at one locus (co-dominance) and Homozygous dominant lethal at another locus			2		4	1	2		2	1
Homozygous recesive lethal at either locus	1	2		2	4
Recessive Epistasis When one gene is homozygous recessive, it hides the phenotype of the other gene. ( aa epistatic to B and b )	9					3		4
Dominant Epistasis When one gene is dominant, it hides the phenotype of the other gene. ( A epistatic to B and b )	12							3		1
Dominant and Recessive Epistasis When either gene is dominant, it hides the effects of the other gene. ( A epistatic to B and b, bb epistatic to A and a, A and bb produce identical phenotypes)	13							3
Duplicate Recessive Epistasis When either gene is homozygous recessive, it hides the effect of the other gene. ( aa epistatic to Bb, bb epistatic to A and a )	9					7
Duplicate Dominant Epistasis When either gene is dominant, it hides the effects of the other gene. ( A epistatic to B and b, B eptistatic to A and a )	15									1
Duplicate Interaction When either gene is dominant, it hides the effects of the other gene. ( A and B interact)	9					6				1