Jacob Sheep Color Genetics

Jacob sheep typically have a base color of black. There are, however, several other colors or shades that occasionally show up as the base color on some individual sheep. These non-black colors are collectively known as lilac—though different descriptive names such as pewter, beige, taupe, etc., have been used by some individual breeders. The genetic controls of these colors have been somewhat of a mystery with personal hypotheses running rampant. This page attempts to explain the genetic factors controlling coat color in Jacob Sheep using only those genetic factors whose existance is currently accepted by the broad scientific community.

Other color genes (alleles) have been suggested, but not satisfactorily proven. These suggested genes may exist, as may others not yet suggested, but until verified their existence is scientifically questionable. (Spotting, ticking, age freckling, and age graying have been ignored in this site.)

Þ To understand Jacob color genetics, one must first realize that lilac is not a single color under a single genetic control, but a group of colors under different genetic controls.

Þ The main genetic factor controlling color in most breeds of sheep is the agouti locus. There are nearly a score of alleles (genes) that are believed by geneticists to reside at this locus (any given sheep has only one pair).

Þ The main genetic factor controlling color in Jacob sheep is the dominant black (E^D) allele at the extension locus. (The “normal” genetic control for black in sheep is the agouti allele (A^a) at the agouti locus. To avoid confusion this agouti allele will be called “recessive agouti black”.) The dominant black allele overrides the expression of the allele(s) at the agouti locus, producing black regardless of the genotype at the agouti locus. (Hence the name dominant black.) In most breeds of sheep the “wild” allele (E⁺) exists at the extension locus, allowing the agouti alleles to be expressed.

Þ The agouti locus is largely ignored in Jacob sheep because of the effect of the dominant black allele. However, as agouti is part of the sheep genome, it must exist in Jacobs—though its alleles are sometimes hard to identify because the dominant black is hiding them. Nearly certainly the agouti locus is occupied by the agouti grey (A^g) allele in some—possibly even most—Jacobs and likely (given the breeds history as a park sheep and the other park sheep it ran with) the recessive agouti black (A^a) exists in at least some Jacobs. (Agouti grey (A^g) is dominant to recessive agouti black (A^a).)

Þ Jacob breeders often assume that Jacobs should be homozygous for dominant black (E^DE^D), and that anything else is evidence of crossbreeding. This assumption is not valid as recessive alleles are difficult—if not impossible—to totally remove from a population, even after hundreds of generations.

Þ Here’s where the tricky part comes. The agouti locus can only be expressed when the extension locus does not contain the dominant black allele, hence the agouti alleles act as if they where recessive alleles at the extension locus. However, since the dominant black and the recessive agouti black have the same phenotype the expected phenotypic ratios are not observed.

Þ To further complicate matters, a third locus is probably involved. The brown locus normally contains the “wild” allele (B⁺) which simply allows the “normal” color of the melanins to be produced. The recessive brown (B^b) allele at this locus causes the normal black melanin to be “bleached” to brown if the animal is homozygous (B^bB^b). (This "bleaching" is actually the effects of hydrogen peroxide accumulating in the melanocytes.)

Þ The agouti, extension, and brown loci should combine to produce the basic colors in the Jacob sheep—black, brown (moorit), grey, and grey-brown (grey moorit). (Or whatever other names people use, as color names are highly subjective.) In addition, there are variations in shades, intensities, etc., of those basic colors, these variations resulting from other factors such as lesser loci and environmental factors .

Þ There are 27 possible combinations of the alleles described above as shown in the following punnett square. These 27 combinations together only produce four colors!

	E^DB⁺A^g	E^DB⁺A^a	E^DB^bA^g	E^DB^bA^a	E⁺B⁺A^g	E⁺B⁺A^a	E⁺B^bA^g	E⁺B^bA^a
E^DB⁺A^g	E^DE^DB⁺B⁺A^gA^g	E^DE^DB⁺B⁺A^gA^a	E^DE^DB⁺B^bA^gA^g	E^DE^DB⁺B^bA^gA^a	E^DE⁺B⁺B⁺A^gA^g	E^DE⁺B⁺B⁺A^gA^a	E^DE⁺B⁺B^bA^gA^g	E^DE⁺B⁺B^bA^gA^a
E^DB⁺A^a	E^DE^DB⁺B⁺A^gA^a	E^DE^DB⁺B⁺A^aA^a	E^DE^DB⁺B^bA^gA^a	E^DE^DB⁺B^bA^aA^a	E^DE⁺B⁺B⁺A^gA^a	E^DE⁺B⁺B⁺A^aA^a	E^DE⁺B⁺B^bA^gA^a	E^DE⁺B⁺B^bA^aA^a
E^DB^bA^g	E^DE^DB⁺B^bA^gA^g	E^DE^DB⁺B^bA^gA^a	E^DE^DB^bB^bA^gA^g	E^DE^DB^bB^bA^gA^a	E^DE⁺B⁺B^bA^gA^g	E^DE⁺B⁺B^bA^gA^a	E^DE⁺B^bB^bA^gA^g	E^DE⁺B^bB^bA^gA^a
E^DB^bA^a	E^DE^DB⁺B^bA^gA^a	E^DE^DB⁺B^bA^aA^a	E^DE^DB^bB^bA^gA^a	E^DE^DB^bB^bA^aA^a	E^DE⁺B⁺B^bA^gA^a	E^DE⁺B⁺B^bA^aA^a	E^DE⁺B^bB^bA^gA^a	E^DE⁺B^bB^bA^aA^a
E⁺B⁺A^g	E^DE⁺B⁺B⁺A^gA^g	E^DE⁺B⁺B⁺A^gA^a	E^DE⁺B⁺B^bA^gA^g	E^DE⁺B⁺B^bA^gA^a	E⁺E⁺B⁺B⁺A^gA^g	E⁺E⁺B⁺B⁺A^gA^a	E⁺E⁺B⁺B^bA^gA^g	E⁺E⁺B⁺B^bA^gA^a
E⁺B⁺A^a	E^DE⁺B⁺B⁺A^gA^a	E^DE⁺B⁺B⁺A^aA^a	E^DE⁺B⁺B^bA^gA^a	E^DE⁺B⁺B^bA^aA^a	E⁺E⁺B⁺B⁺A^gA^a	E⁺E⁺B⁺B⁺A^aA^a	E⁺E⁺B⁺B^bA^gA^a	E⁺E⁺B⁺B^bA^aA^a
E⁺B^bA^g	E^DE⁺B⁺B^bA^gA^g	E^DE⁺B⁺B^bA^gA^a	E^DE⁺B^bB^bA^gA^g	E^DE⁺B^bB^bA^gA^a	E⁺E⁺B⁺B^bA^gA^g	E⁺E⁺B⁺B^bA^gA^a	E⁺E⁺B^bB^bA^gA^g	E⁺E⁺B^bB^bA^gA^a
E⁺B^bA^a	E^DE⁺B⁺B^bA^gA^a	E^DE⁺B⁺B^bA^aA^a	E^DE⁺B^bB^bA^gA^a	E^DE⁺B^bB^bA^aA^a	E⁺E⁺B⁺B^bA^gA^a	E⁺E⁺B⁺B^bA^aA^a	E⁺E⁺B^bB^bA^gA^a	E⁺E⁺B^bB^bA^aA^a

Þ These 27 genetic combinations produce the four colors found in Jacobs. Fourteen produce black, seven produce brown, four produce grey, and two produce grey-brown. (These numbers do not represent the actual ratios in the Jacob sheep population as some alleles—particularly E⁺—have likely been selected against, whether intentionally or not, by Jacob breeders.)

E^DE⁺B⁺B⁺A^aA^a	\|\|	Black (dominant)
E^DE⁺B⁺B⁺A^gA^a	\|\|\|\|	Black (dominant)
E^DE⁺B⁺B⁺A^gA^g	\|\|	Black (dominant)
E^DE⁺B⁺B^bA^aA^a	\|\|\|\|	Black (dominant)
E^DE⁺B⁺B^bA^gA^a	\|\|\|\|\|\|\|\|	Black (dominant)
E^DE⁺B⁺B^bA^gA^g	\|\|\|\|	Black (dominant)
E^DE^DB⁺B⁺A^aA^a	\|	Black (dominant)
E^DE^DB⁺B⁺A^gA^a	\|\|	Black (dominant)
E^DE^DB⁺B⁺A^gA^g	\|	Black (dominant)
E^DE^DB⁺B^bA^aA^a	\|\|	Black (dominant)
E^DE^DB⁺B^bA^gA^a	\|\|\|\|	Black (dominant)
E^DE^DB⁺B^bA^gA^g	\|\|	Black (dominant)
E⁺E⁺B⁺B⁺A^aA^a	\|	Black (recessive)
E⁺E⁺B⁺B^bA^aA^a	\|\|	Black (recessive)
E^DE⁺B^bB^bA^aA^a	\|\|	Brown (on dominant and recessive black)
E^DE^DB^bB^bA^aA^a	\|	Brown (on dominant and recessive black)
E^DE⁺B^bB^bA^gA^a	\|\|\|\|	Brown (on dominant black)
E^DE⁺B^bB^bA^gA^g	\|\|	Brown (on dominant black)
E^DE^DB^bB^bA^gA^a	\|\|	Brown (on dominant black)
E^DE^DB^bB^bA^gA^g	\|	Brown (on dominant black)
E⁺E⁺B^bB^bA^aA^a	\|	Brown (on recessive black)
E⁺E⁺B⁺B⁺A^gA^a	\|\|	Grey
E⁺E⁺B⁺B^bA^gA^a	\|\|\|\|	Grey
E⁺E⁺B⁺B⁺A^gA^g	\|	Grey (homozygous, possibly lighter)
E⁺E⁺B⁺B^bA^gA^g	\|\|	Grey (homozygous, possibly lighter)
E⁺E⁺B^bB^bA^gA^a	\|\|	Grey-brown
E⁺E⁺B^bB^bA^gA^g	\|	Grey-brown (homozygous grey, possibly lighter)

Þ Given the large number of genotypic combinations that can produce each color it is difficult, if not impossible, to predict the results of a cross between any two specific sheep without knowing their genotype. Similarly, in most cases general statements such as "this color crossed with that color should give . . ." are highly untenable.