• Created by: rosieevie
  • Created on: 22-05-17 14:45


Epistasis - modification of dihybrid inheritance by interaction of genes (NOT ALLELES)

Same as dihybrid inheritance but genes interact

F1 same as one dominant parent but new phenotypes in F2

F2 = 9:3:3:1 ratio but can be modifications 

Epistasis often involves pigment pathways

1 of 8

Recessive Epistasis

Sequential biosynthetic pathways

Example - labrador fur colour 

  • A - dominant black fur
  • a - recessive brown fur
  • B - allows pigment to be deposited
  • b - prevents deposition of dark pigment so yellow fur
2 of 8

Dominant Epistasis

One dominant allele produces same phenotype regardless of allelic status of other

Example - squash colour

If W = white squash as enyzme I cannot be activated and convert to green squash

If w = green squash as enzyme I can be activated

If wwY = yellow squash as enzyme B can be activated and convert to orange


3 of 8

Reciprocal/Duplicate Recessive Epistasis

Both dominant alleles from each gene required for pigment to occur

Example - albinism in snails

1 dominant activates Enzyme I = still white

2 dominants activates Enzyme I and B = colour pigmentation


4 of 8

Duplicate Genes with Cumulative Effect

Effect of both dominant alleles additive so individual dominant alleles have same effect

No dominant alleles have no effect

Example - fruit shape in squash

  • Both domiannt = white round
  • 1 dominant = Green round
  • Both recessive = Orange curvey weird round
5 of 8

Duplicate Dominant Gene

Both dominant alleles have identical effect but no additive effect 

Example - seed capsule shape in Shepherds purse

Gene A and Gene B both activate different enzymes that do the same thing


6 of 8

Dominant and Recessive Interaction

Dominant allele from one gene and recessive allele from other have same phenotype

Gene A can suppress expression at B gene


7 of 8

Quantitative Inheritance

Multiple alleles - gene locus has more than 2 alleles

  • Example - mammal coat colour, blood type

Multiple genes - each gene with two alleles

  • Example - skin pigmentation
8 of 8


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Genetics resources »