This is an update with photos of an article originally posted April 17, 2011.
Not all horses with the leopard gene have blankets of any size, and not all have spots. The gene can also produce two specific types of roaning, called frost and snowflake.
These roan patterns are quite separate from that produced by the roan gene, which becomes less prominent with age and leaves head, legs, mane and tail dark. The leopard gene produces horses which are normally colored or at most have a few white hairs over the rump at birth, but develop roaning (frost) or scattered white spots (snowflake) as they age. In contrast to grey, the pattern eventually stabilizes rather than producing a pure white horse.
In frost, the roaning tends to be most prominent over the hips. So-called varnish marks are common — areas where the bones are close to the surface, such as the hipbones and nasal bones, retain pigment while the rest of the coat is roaned. An aged varnish roan may be almost white except for these varnish marks.
Snowflakes are small white spots scattered randomly over the body, but often most numerous and prominent on the front part of the horse. They tend to become larger and more numerous with age, until in extreme cases the horse appears white with colored specks. This gives what is often called a speckled pattern, not to be confused with flea-bitten grey. Note that not all of the photos shown at the link are true snowflakes — the term is used very loosely.
Both types of roan may be combined with any of the blanket or spotting patterns, or may occur alone or together. Figure 8.140 in Sponenberg is a beautiful example of a combination of snowflake, varnish roan, blanket and leopard spotting all on the same horse. (Put Figure 8.140 on the search inside field.) Since the leopard gene can produce any of these effects, alone or in combination, breeding leopard-pattern horses can lead to some interesting results.
The remaining named horse in Tourist Trap, Amber’s mount Splash, is a bay varnish roan with a small spotted blanket, in color rather like the horse on the left side, but with black points and no blaze. He’s a gelding, about 14.2 hands – just enough smaller than the other four to have problems with fords. Roi has seen only solid colored horses on Central, and his first look at Splash gives this impression:
“Amber’s [horse], a little bay roan with curious dark lines on its nose, looked less exotic until it turned as she halted it. Then it became apparent that it had a large white area, punctuated by dark bay spots, over its hips.”
I will summarize the equine color loci and alleles next week with links back to where they are mentioned, but I have covered most of the known color genes in horses. That doesn’t mean more won’t be found!