Horse Color Genetics: The Basics

I have done a ton of research on genetics recently (sort of all in one day; I had the urge to know all at once). I got started because breeding was on my mind. I have thought about breeding my horse Chocolate. There is a great website where you can type in the color of two different horses, and it will give you the different color combinations it will make. That was really fun to play around with.

I'm not really sure what made me interested in the science behind the color, but all of a sudden I really, really wanted to know why Chocolate was solid black, and not spotted like both of her parents.

A great way to explain how genetics work is by using flowers. This is not my own example, I read this somewhere, but I will paraphrase it. Pretending flowers can breed (which they obviously can not), say you bred a red flower with a blue flower. Each flower has two genes in it. The red has two red genes, and the blue has two blue genes. The resulting flower needs one from each, one red gene and one blue gene. Mixed together, it makes purple! Because there are now two genes inside of it, that does not mean that is has two purple genes, the genes are still red and blue. Now, if that purple flower bred with a red flower, the genes from the purple flower still have to split. This means that the 'baby flower' is going to inherit one red gene from the red flower, but it could inherit a red or a blue gene from the purple flower. Make sense? The result is either a red flower or a purple flower. 

Still using the flower example, the first two flowers were red and blue. We knew that both flowers had two of the same color gene. In horses, this is called homozygous; it means that we know exactly what will be inherited by resulting foals. If the flower had one gene of each, like the purple flower, and it had to pass on only one of the genes, this is called heterozygous. Homozygous means both genes for a certain color are dominant or recessive. 

Dominant and recessive is basically saying whether or not your horse has something. If a horse is dominant homozygous black, or EE, that horse is black, and we know that any foals, regardless of the other parent, will receive one dominant black gene. If a horse is heterozygous black, or Ee, that horse is still black (they only need one dominant gene to make it black), and it means the resulting foal may or may not receive that black gene. Remember, each gene has to split, so if it got the E part (the dominant gene) then it would be black, but if it got e (recessive), then it won't be black unless it got a black gene from the other parent.  And lastly, if a horse is recessive homozygous black,or ee, it means we know that the foal will not receive any black from that parent.