Equine Color Genetics: Grey and Roan

Grey

This is a grey horse, she was born a solid color, like her foal, however over the years white hairs have filled in and she has “turned grey”. Her photo is from Wikimedia. Grey horses are always born colored, and turn grey over time, some faster than others. Grey is a dominant gene, meaning if a horse even only has one grey gene it will be grey. Therefore a grey horse could be GG or Gg. If you can look at its’ pedigree you might be able to determine what it is. If one parent is grey and one is not, then the horse is Gg.  If it produces a foal that does not turn grey, you know that it is Gg, as otherwise it could only produce grey foals if it were GG. A non-grey horse is always gg.

This chart demonstrates what would happen if you bred a grey horse who is Gg with a non-grey horse. The grey horse is represented on the top as Gg, the non-grey is on the side. The letters are carried forward into the boxes, and we see the resulting combination is that half the time this pairing will result in a grey, Gg foal, and half will result in a non-grey, gg, foal. If you do the same with breeding a horse who has two grey genes, GG to a horse that is non grey, gg, you will notice you will always get a grey offspring, Gg. Two non-greys can never produce a grey when bred together.

Note:

The color grey in donkey’s is different, they do not change over time, a grey donkey is born a solid tone of grey and remains that way for his or her life. Their genetics are entirely different.  This is my photo. 

Click here to read about the genetics of Cremello, Palomino, and Chestnut.