Shimmer switch and expression

Shimmer is a complex combination of modifier genes, where the switch gene (SH) decides if shimmer shows or not, and the expression genes (R/r, J/j, S/s) determines the colors of the shimmer. For shimmer to show, one or two copies of shimmer is required (SHSH or SHsh) and at least one expression gene.

Expression genes are noted as uppercase when active, and lowercase when not active. For example in order for a ruby shimmer to show, the ruby gene has to be RR or Rr, while rr doesn't produce any ruby shimmer.

If a horse doesn't have any shimmer or any expression genes (shsh(rr/jj/ss)) it can be completely omitted from the genotype. That means all genotypes without any switch or expression genes are shsh(rr/jj/ss) by default (and thus doesn't have to be listed in the genotype).

If a horse has either switch or expression genes, but not both, e.g. SHSH(rr/jj/ss) (switch but no expression) or shsh(Rr/JJ/ss) (expression but no switch), it will not show any shimmer at all, and the phenotype will describe it as “carries shimmer”.

Expression combinations

Shimmer expression genes consist of Ruby (RR, Rr, rr), Jade (JJ, Jj, jj), and Sapphire (SS, Ss, ss). Together they can create a total of 7 different combinations:

Ruby - (R_/jj/ss). Has one or two copies of R only.

Jade - (rr/J_/ss). Has one or two copies of J only.

Sapphire - (rr/jj/S_). Has one or two copies of S only.

Ember (Ruby + Jade) - (R_/J_/ss). Has one or two copies of both R and J.

Orchid (Ruby + Sapphire) - (R_/jj/S_). Has one or two copies of both R and S.

Lagoon (Jade + Sapphire) - (rr/J_/S_). Has one or two copies of both J and S.

Prismatic (Ruby + Jade + Sapphire) - (R_/J_/S_). Has one or two copies of all 3 expression genes.