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  • Created by: Steff06
  • Created on: 24-04-16 18:00

Epistasis meaning and explanation

Epistasis = Interaction of different gene loci.

One gene locus masks or surpresses the expression of another gene locus. 

The genes involved may control the expression of 1 phenotypic characteristic by either:

  • Working AGAINST each other (ANTAGONISTICALLY) resulting in masking.
  • Working TOGETHER in a complementary fashion.

Working antagonistically:

  • Homozygous presence of a recessive allele may prevent expression of another allele at a second locus. 
  • Alleles at 1st locus are epistatic to alleles at the 2nd locus (hypostatic). 

Epistasis reduces phenotypic variation. 

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Recessive and dominant epistasis


  • E.g. a homozygous aa may be epistatic to alleles of the gene B/b. 
  • Neither the B or the b can be expressed if there is no dominant allele A present.


  • Occurs when a dominant allele at one gene locus masks the expression of the alleles at a 2nd gene locus. 
  • E.g. two gene oci D/d and E/e. Presence of one D alleleresults in whire fruits regardless of the aleles present at the 2nd locus. 

Working in a complementary fashion:

  • The way 2 gene loci may produce these results is if they compliment each other. 
  • If one gene codes for an intermediate colourless pigment and the second locus codes for an enzyme that converts the intermediate compound to the final purple pigment. 
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