Coat color genetrics part IV: E-locus (Extension)

by Annika Farstad
© 2006

The Extension Locus is a pattern Locus.
It allows or restricts the extension of dark pigment.


(E) Extension Normal:
Full extension of dark pigment as dictated by the A & B locus. This means that any black hairs the dog may have on his coat will be visible. If a dog carries E it will be black coated unless it also carries the two recessive genes for liver, in which case it will be liver coated.


(E^M) Extension Mask:


(e) Extension Yellow:
(also called ee red, recessive red/yellow or true red) Restricts the appearance of any black pigment. This gene only affects black pigment (Eumelanin), not yellow/red (Phaeomelanin) - creating a recessive yellow (red/cream) with no black in the coat. It also means that what could effectively be a genetically black dog can look cream or red. This is the only time that two red/cream dogs can produce a black puppy it means that they are genetically black but the black colour is restricted by the ee.

The skin and eye color generally show through normally but some ee dogs will show reduced pigment on the nose giving the dog what is termed a snow (fades to pink in winter) or dudley (fades to pink all year round) nose. They also seem to be more heavily affected by any gene modifier that reduces pigment.