Epistasis

1
Epistasis

• An interaction between nonallelic genes,
  especially an interaction in which one gene
  suppresses the expression of another.
• A film that forms over the surface of a urine
  specimen.
• The suppression of a bodily discharge or
  secretion.

2
Epistasis vs Dominance

• Epistasis is not the same thing as dominance.
  With epistasis, a mutation in one gene masks the
  expression of a different gene. With dominance,
  one allele of a gene masks the expression of
  another allele of the same gene.

3
For example
Horses are capable of producing two basic
pigments within the hair shafts. These pigments
are determined by the Extension locus (E).
E Eumelanin black pigment e Pheomelanin
red pigment.
ee
EE or Ee
However, there is another locus involved in hair
color. The Agouti locus (A) controls where on the
horse the black pigment shows up.
A Black pigment restricted to certain areas
a no effect
AA or Aa
aa
4
The E locus is epistatic to (or masks) the A
locus. The A locus is hypostatic to (or is
masked by) the E locus. For example A
horse whos genotype is ee has no black pigment.
Therefore, the A locus, which controls black
pigment, has no effect, regardless of what
alleles the horse has. Note Even if a locus
doesn't have any visible effect, the horse still
caries alleles at that locus. Therefore, those
alleles may not show until the right conditions
occur in a later generation.
5
References

• epistasis. (n.d.). The American Heritage
  Dictionary of the English Language, Fourth
  Edition
• http//www.sci.sdsu.edu/smaloy/MicrobialGenetics/
  topics/genetic-analysis/epistasis.html
• http//www.mhref.com/color/genetics/tour/basic5.ht
  ml