Updated 29.3.2018 to include more research!
Please note I published this under a noncommercial Creative Commons license. Feel free to share if you find it useful or interesting!
This is a chart on the possible colours of Eurasian wild horses or tarpans (Equus ferus ferus
) - a surprisingly varied population, as shown by ancient dna and cave art. These animals only went extinct around year 1900.
Depicted is a selection of possible combinations of the alleles known to have been present in wild tarpans. According to the data set of Pruvost et al. (2011), the most common colours were bay dun, grullo, and spotted bay dun - marked with blue circles in this chart. All these seem to be also depicted in European cave art. According to Imsland et al. (2016) the dun allele was also polymorphic in wild horse population, causing some individuals to be darker than others.
Different combinations would have necessarily occurred from time to time, when horses of different colours mated. The Lp allele, producing leopard spotting, is affected by a large number of modifiers, only one of which of which have been tested on ancient horses. That was only in domesticated Botai horses (Gaunitz et al. 2018). I depicted a variety of possible outcomes of it, but it's impossible at the moment to be sure which spotting patterns were really present.
The letters underneath each horse refer to their alleles. These four were polymorphic in the tarpan population:
A - dominant allele causing brown coat
a/a - recessive allele causing black coat
E - dominant allele enabling black in coat and mane
e/e - recessive allele preventing black coat and mane (result being a chestnut horse)
D - dun, a diluting factor present in wild horses and asses. Causes lighter coat colour and primitive markings (two-coloured mane, stripes etc.)
d1/d1 - recessive allele causing non-dun colour (black, bay, or chestnut, depending on the base colour). Leaves some primitive markings visible.
Leopard / varnish roan locus
lp/lp - no leopard complex, no spots
Lp/lp - leopard complex, spotted
LP/LP - leopard complex, mostly white. There is a night vision defect associated with homozygous animals, probably making them vulnerable to predators.
I had to assume this one, since genetic test for it was onlt developed in 2016 and it hasn't yet been widely tested on ancient horses:
PATN1 - patterning factor, causes leopard spots with LP