Update on the Single Gene Gray Mouflon
by Margaret Flowers
Since 2010, readers of the ISBONA Newsletter have been following the progeny of the“single gene gray mouflon” (sggm) pattern (registered with CLRC as “6”) that appeared unexpectedly at Fence Row Farm as the result of a cross between a gray/solid (patterns “2/5”) x badgerface/solid (patterns “3/5”). Two questions came from this: where did the pattern come from, and how is it inherited? Initial crosses made by Marty Favre suggested the possibility that the sggm allele was recessive to all others, as the only sggm lambs from the originating ram (Xeno) came from crosses with half-sibs, and unrelated solid ewes produced only solid lambs. Subsequently, an sggm ewe was born on another farm from an unrelated solid ewe. That same year Xeno also sired a sggm ewe from an unrelated solid black ewe.
In 2013, lambs from Xeno or his offspring were born on at least four farms. My thanks to Marty Favre, Elaine Clark and Terri Carlson for sharing information about their breeding. On these farms, there were three breedings made between an sggm (“6”) rams x solid (“5”) ewes; from these, there were 3 sggm and 3 solid lambs (one of each pattern from each cross). There were also two breedings (on different farms) with a solid ram and sggm ewe, two of which produced a single sggm lamb (Figure 1).
So….
sggm x solid --> sggm + solid and
solid x sggm --> sggm + solid
Figure 1. Ewe showing the sggm pattern. Note the classic mouflon markings around the eyes, and the slight amount of sugaring at the lips and light thel showing through the tog. (photo by Terri Carlson.
In addition, there were two crosses made between sggm rams and white (“1”) ewes (different farms). One of the ewes is known to be homozygous white, and the other may well be. All the lambs from both of these breedings were white.
So…
sggm x white --> white (unknown at this time whether the second allele is sggm or solid)
Finally, there were two breedings between an sggm ram and badgerface (“3”) ewes, and a breeding between the same sggm and a gray (“2”) ewe. One of the badgerface breedings resulted in a solid (“5”) ram and sggm (“6”) ewe; the otherproduced a solid ram (“5”) and a badgerface gray-mouflon (“3/6”; Figure 2), with both patterns expressed. Likewise, the sggm x gray breeding resulted in a solid ram and a ewe that is sggm, co-expressing gray (“2/6”; Figure 3).
So…
sggm x gray --> solid + gray-sggm and
sggm x badgerface --> solid+ sggm + badgerface-sggm
Figure 2. Sggm ram, co-expressing badger. Note how the badger and mouflon patterns counteract each other. (photo by Terri Carlson)
Figure 3. Sggm ewe, co-expressing gray. Note the white eye spots, and the much more definite “sugar lips.” (photo by Terri Carlson)
This is an exciting development in our understanding of the inheritance of the sggm trait. In his important work on color inheritance in Icelandic sheep, and based on limited information because of the rarity of the trait even in Iceland, Adalsteinsson demonstrated that the sggm (pattern/allele 6) was recessive to the white pattern and dominant to the solid.
Moreover, when considering the data from the numerous crosses made between different genotypes of Icelandic sheep, Adalsteinsson concluded that inhibition of pigment production was dominant, and that different patterns were the result of this inhibitory action on different parts of the sheep, and on different follicle types (i.e. at different times) during fetal development (Table 1).
Table 1. Effect Of Alleles A1 – A6 On Pigment Production By Body Regions And Follicle Types. (from Adalsteinsson, p. 113)
a primary follicles produce tog fibers
b secondary follicles produce thel fibers
c - = absence of black or brown pigment
d + = presence of black or brown pigment
Thus, Adalsteinsson concluded that the gray-mouflon pattern (sggm - A6) would be dominant to gray (A2), mouflon (A4), and solid (A5) and recessive only to white (A1), and that badgerface (A3) and gray-mouflon were neither dominant nor recessive to one another – in other words, were co-dominant.
The recent breeding data by ISBONA members stongly suggests that sggm is recessive to white and confirms that it is dominant to solid, and is also co-dominant with badgerface. However, the existence of the sggm that co-expresses gray suggests that sggm and gray may also be co-dominant. This should not be unexpected because animals that are homozygous for gray are considerably lighter than those that are heterozygous (indicating perhaps that the dominance is not absolute?) Additional breeding will be needed to confirm these inheritance patterns, and to determine conclusively the dominance of white, and whether an animal that is sggm/mouflon (A6/A4) will also express the mouflon trait in some way. Our information to date suggests that members of ISBONA have made a breakthrough in pattern inheritance of the Icelandic sheep. Congratulations!
Now…to figure out where it came from. Most likely a mutation…but what kind, and on what chromosome? Any molecular geneticists out there who would like to take on this little project?
The breeding information provided by Marty Favre, Elaine Clark, Terri Carlson is gratefully acknowledged. Thanks also to Marty Favre and Linda Schwab for their review of drafts of this paper and for their most helpful suggestions.
Literature Cited
Adalsteinsson, Stefan. 1970. Color inheritance in Icelandic sheep and relation between color, fertility and fertilization. J. Agr. Res. Icel. 2(1):3–135.
Published in the Winter, 2014 issue of the ISBONA Newsletter.
Stalking the Single Gene Gray Mouflon
by Margaret Flowers
Readers of this Newsletter, as well as followers of the ISBONA and Icelandic Owners Facebook pages, have had the opportunity to read about and discuss the rare pattern mutation (SGGM) that appeared unexpectedly in a ram (FAV RAM XENO B6H 31X) in Marty Favre’s flock (Fence Row Farm, Charlotte, MI). With the appearance of this pattern, there have been careful attempts by members of this Association to determine the pattern of inheritance relative to the other pattern alleles (white, gray, badgerface, mouflon, solid). In a Winter, 2014 Newsletter article, we can find a fairly complete picture of this inheritance, but with a couple missing pieces.
From crosses made by ISBONA members, SGGM has been demonstrated to be co-dominant to gray and badgerface, and dominant to solid. Gray, badgerface and mouflon are all cdominant, so it is reasonable to assume that since SGGM has been demonatrated to be co-dominant to gray and badgerface, it is also co-dominant to mouflon. But is it? More about this later.
We also know that animals heterozygous for SGGM (say, SGGM/solid), when bred to white, have produced white progeny. In making this cross in his seminal work on pattern and color inheritance, Adalsteinsson very reasonably assumed that SGGM was recessive to white. However, to prove this, it must be demonstrated that the allele hidden by the dominant white was SGGM and not solid (or other pattern) carried in the SGGM animal. As of this spring, we now have the needed evidence to determine the dominance relationship between SGGM and white patterns.
Erin Braaton (Dancing Aspens Farm, Kalispell, MT) bred a white ewe to a ram that was SGGM. This pair produced a white ram (named Hero). Last fall, Erin bred Hero to a black-gray spotted ewe. The result is IZZY, a ewe lamb, expressing both gray and SGGM (this co-expression of gray and SGGM was reported earlier by Terri Carlson of Red Brick Road Farm, Dixon, IL), and is illustrated in the Winter 2014 Newsletter. Erin’s ewe lamb could only have inherited the gray pattern allele from the dam; the SGGM was inherited from the sire, where it was covered by white pattern. Thus, with the birth of this lamb, we can conclusively say that White pattern is dominant over SGGM. We have been able to prove what Adalsteinsson surmised.
The only remaining issue of pattern inheritance is that of the relationship between SGGM and mouflon. Co-dominance seems to be a tricky thing. When one allele is gray, and the other badger, the animal we see is distinctively a gray-badger. Similarly we can recognize gray-mouflon and badger-mouflon. So, since both alleles are expressed, we can say that they are co-equal; both are active. However, we see a different picture when we look at double doses of these alleles. Homozygous gray is distinctly lighter than heterozygous gray; both of the alleles must be active, and the effect of their presence is sdditive. This is the same situation as with co-dominance between different patterns (e.g., gray/badger), so in some sense we can say that gray is co-dominant with itself as both pattern (gray) alleles are expressed. But what happens with a double dose of badgerface, or a double dose of mouflon? How does one distinguish homozygous from heterozygous? I’ve asked a number of breeders, and the answer seems to be….it’s not possible. Colors seem to be no more intense, and markings and color boundaries no sharper.
Given this situation, is it possible to say anything about the dominance relationship between SGGM and mouflon? This year Terri Carlson’s SGGM ram produced a lamb that is mouflon. This ram clearly had one SGGM and one mouflon allele at the pattern locus (SGGM/mouflon), and the lamb inherited the mouflon from the sire. While this does not prove that SGGM and mouflon are co-dominant or if SGGM is dominant to mouflon, what it does tell us that mouflon is not dominant over SGGM.
So what we now know:
White is dominant to SGGM
SGGM is co-dominant with gray and badger
SGGM is either co-dominant with or dominant to mouflon
SGGM is dominant over solid
One more piece of the SGGM genetics puzzle is now in place!
Literature Cited
Adalsteinsson, Stefan. 1970. Color inheritance in Icelandic sheep and relation between color, fertility and fertilization. J. Agr. Res. Icel. 2(1):3–135.
Published in the Summer, 2016 issue of the ISBONA Newsletter.
An additional note:
The recently-published book, Icelandic Sheep--Colorful All-Rounders, suggests that the rare gray-mouflon allele is possibly extinct now in Iceland; indeed, from the small number of crosses that Adalsteinsson was able to make, it was a rare occurrence in the flock in 1970. In North America, on the other hand, the population of SGGM sheep is expanding, thanks to the breeding efforts of an increasing number of farms.