“Lavender is a dilution factor present in Jacobs,” explains Liz. “Its expression appears to require the presence of a dominant black genotype. There are two kinds of genetic black in sheep: a recessive version, which is widespread and occurs in many breeds, and a dominant black, present in just a few. Balwen and Blue Texel, for example, have a recessive black. The colour of Jacob and Zwartbles is due to dominant black.
“There is some variation in intensity of lavender colour. We are not sure what the influence(s) is/are. It is possible that the lavender shade differs according to whether the individual is homozygous (having two of the same allele, an allele being different forms of the same gene) or heterozygous (having one each of two different alleles) for dominant black. It is thought that the lavender genotype does not show well on a recessive black genotype.”