Loki is a mostly-white foal who was entered into our Mystery horse competition. His dam is a Palouse pony, and his sire is unknown.

We tested Loki for a wide range of colour genes to find out why he is nearly completely white, and why coloured bits are such an unusual colour too.

Lets start with the few parts of Loki that aren’t white. We tested Loki for agouti, red/black, cream, silver and dun. This showed that he is a silver dapple (silver on a black base). His genotypes were ‘a a’ for agouti, ‘E e’ for red/black, and ‘Z Z’ for silver – yes, he is actually homozygous silver. The other dilution genes were negative.

To look at his white markings, we tested him for all the white pattern genes relevant to his apparent breed: Appaloosa, PATN1, grey, roan, Sabino 1, W20, frame overo, tobiano and splashed white 1 (SW1).

He is a fewspot (i.e. ‘Lp Lp’) with one copy of PATN1. He is negative for all of the other white marking genes we tested.

The effect of the PATN1 gene can only be seen on horses that are also positive for Lp. Most horses with Lp and PATN1 have a lot of white. It’s not a guarantee though – PATN1 is a marker, which means it is strongly associated with lots of white but doesn’t necessarily cause it.

Horses that are negative for Lp that have the PATN1 gene don’t have any special markings that indicate that they have this gene.

Having had a look at his colour genetics, we will also take a brief look at what these results tell us about his health.

All horses with two copies of the Lp gene (including Loki) are night-blind. This means their vision is very poor in low light conditions such as dusk and night time. For owners wondering about how to help their night-blind horse be safe and confident, the Appaloosa Project has a lot of information.

Horses with the silver gene can also have multiple congenital ocular abnormalities (MCOA). This condition, which includes a wide range of potential eye abnormalities, occurs in some silver horses but not all. Horses with two copies of the silver gene – including Loki – are more likely to have MCOA than horses with one copy of the silver gene. It’s not a bad idea to get a homozygous silver horse’s eyes checked by the vet, particularly if you are hoping they will be a riding horse