Over the last 9 months I’ve been pondering how Brea could produce a black lamb. I think I’ve finally figured it out. It requires switching to the Shetland/Icelandic/Finnsheep mindset where white is not a color in the same way black and brown are. In their systems a better term would be the whitewash gene – and (warning, genetic speak to come) and it is at a separate location on the sheep’s chromosome than the black/brown gene’s location. The whitewash gene comes in 2 versions (a.k.a. alleles): W = will cover any other color gene and keep it from being expressed, and w (small w) which will allow the black/brown gene locus to be expressed. Under that system, black and brown are 2 alleles at the color locus, with black (B) being dominant to brown (b). Brea’s genetic makeup (genotype) can be inferred from her offspring when crossed with the perfect test genotype: wwbb. Since these loci are distributed independently (we assume, until proven otherwise), there is equal chance for either allele at the whitewash locus to get passed with either allele at the color locus. The chart below shows how Brea must have one black (B) and one brown (b) allele at the color locus and have one W and one w allele at the whitewash locus. Tioga, the sire to the triplets, was brown. Thus, he had to be bb since both color alleles need to be b in order for brown to be expressed and he had to be ww at the whitewash locus or else he would have been white since W is dominant. A basic premise in genetics is that each parent passes only one allele at each locus/gene to an offspring. Brea has 2 different alleles at each locus (= heterozygous) so can produce eggs having 4 different combinations. The appearance of the offspring is the interplay of all the alleles at both of the loci (plural of locus). In the figure below, the row under Brea’s name represents the 4 possible allele combinations Brea can produce. Tioga can only produce one type of gamete/sperm genotype (genetic package) see second column from left. The first row below Brea’s genetic contributions is a row showing the lamb’s genetic makeup when her eggs are combined with Tioga’s genetic contributions. The second row down is the appearance – in this case lamb color – produced by the interplay of the alleles and genes. The third row is the triplet who has that genetic makeup. Note – because the dominant whitewash gene, W, overrides the color gene we have no way of knowing Dazzle’s color genotype UNTIL she is bred to a wwbb ram and we can view their lambs. We know she is a carrier of the brown allele, because she had to get one from her dad. Sorry for the layout. I couldn’t upload my Excel version of the chart. Clear as mud??? At least it doesn’t have to bug me any more!

The fun thing is… this also explains some odd outcomes from breeding Babydolls where only the B allele exists at the color locus (it’s “fixed”, in genetic terminology). Many years ago Fergie (black) gave me twins, one black and one white, when crossed to a black ram. I had sort of adopted a single gene model and where white is dominant to black, and I could not figure out how 2 blacks could make a white. In light of this alternate model, here is the explanation. Fergie’s mom was white, so she must have been heterozygous at the whitewash gene – Fergie received a w from her mom. Over the years Claire, Nina, Olivia, and Audrey have produced black lambs so are are all Ww.  Sara must be, too, since her father was black (J. C.). Eureka! Science works!