Sunrise Sheep & Wool

Genetic Codes for Icelandic Sheep

At Sunrise Sheep & Wool we have been studying the genetics of colors and patterns in Icelandic sheep for the past few years. To aid us in our breeding program, we have prepared the following keys to the sometimes confusing world of genetic codes. Brent Nelson is the genetic specialist on our farm, who prepared these keys, and who finds the world of Icelandic genetics to be fascinating. In addition to this table, we have prepared a collage of pictures, illustrating some of the different colors and patterns of Icelandic sheep.

Key to Phenotype Codes

The abbreviation for a phenotype indicates the color, pattern, spotting and horned status of a sheep. Letter/number codes are used in the following order: color patterns spotted horned

Phenotype Codes
Code Letters
B = black
M = moorit
O = unknown (hidden by white pattern)
patterns *1
1 = white
2 = grey
3 = badgerface
4 = mouflon
5 = solid
S = spotted
no S = not spotted
H = horned
C = scurs (fixed stubs or very short horns that curl inward)
P = polled (no horns or small, loose stubs)
  • 1 Two pattern codes are required when co-dominant alleles are both expressed. So a sheep with both a badgerface and a mouflon allele [Ab/At] would express both and the phenotype letters would be 3,4. A grey mouflon, whether [Agt/A?] or [Ag/At], would be 2,4.

Key to Genotype Codes

There are three main loci that affect the appearance of a sheep's fleece:

S locus (spotting) If an animal is spotted, color will be turned off in the spotted area, making white spots. The effect of spotting is dominant over all patterns and colors. Almost the entire sheep may be spotted, with only colored eyerings. A white sheep with spotting will have whiter fleece in the spots.
A locus (pattern) There are several possible agouti alleles, some of which are co-dominant with each other. The effect of a pattern is dominant over all colors, with different patterns turning off the primary color in different places, leaving a white pattern.
B locus (color) The primary color is black or moorit (brown).

A (Agouti or Pattern) Locus
Allele Code Name Co-Dominant with Dominant to Description
Awt White (none) Agt, Ag, Ab, At, Aa Solid white sheep.
Agt Grey Mouflon (Iceland) (none) *1 Ag, Ab, At, Aa Grey upper body (colored tog, white thel). Colored head, legs, tail. White throat, belly, under tail. Sugar lips (white). White inside ears. White eyebrows.
Ag Grey Ab, At Aa *2 Grey body (colored tog, white thel). Colored head, legs, tail. Sugar Lips (white). White inside ears.
Ab Badgerface Ag, At *3 Aa White upper body. Colored belly. Colored head with white mask across nose.
At Mouflon (Reverse badgerface) Ag, Ab Aa Colored upper body, head, legs, tail. White throat, belly, under tail. White inside ears. White eyebrows.
Aa Solid (none) (none) Solid color.
  • 1 There are conflicting reports on the web regarding whether Agt is co-dominant with Ab.
  • 2 It is possible that Ag is incompletely dominant over Aa, where [Ag/Ag] appears greyer than [Ag/Aa].
  • 3 A badgerface mouflon [Ab/At] will appear white with a line of color where the two patterns don't quite meet on the rear leg or buttocks.

B (Color) Locus
Allele Code Name Dominant to
BB Black Bb
Bb Moorit (brown) (none)

S (Spotting) Locus
Allele Code Name Dominant to
SS Not Spotted Ss
Ss Spotted (none)

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Updated: May 8, 2007 by David A. Nelson   (Sunrise Sheep & Wool)