Genetics Basics
I am going to make this as easy as possible for anyone to understand, even if you do not have a scientific understanding of genetics. Animals get two genes, one from their mother, one from their father, for everything. There are many, many, genes involved in controlling colors. So while reading this remember these are only two sets of genes that a horse would have that help determine color.
To help explain how genetics work I will reference one of the best known genes, the XY genes. These are the ones that determine gender in all animals. Females are XX, Males are XY. When reproduction takes place, each parent gives one of each of its' gene pairs. Females can only give the X gene, males can give the X or the Y gene, it is a 50/50 chance which they give, therefore a 50/50 chance if the baby is going to me male or female. The mothers unfertilized egg would carry only one X gene for gender, the males sperm would have either one X or Y, when they unite the egg now has two genes for that pairing and the gender is determined by which pairing it was. Eggs and sperm also have each of every other gene sequence, for now we will talk about the roan and the grey gene, these are two separate genes.
This horse is a Chestnut
The color of chestnut is typically an orange brown shade, with no black markings. This color is seen in many breeds. The photo is from Wikimedia.
This horse is a Palomino
The color of Palomino is a beige colored body with a lighter, or near white, mane and tail. They also have no black markings. The photo is from Wikimedia.
This horse is a Cremello
This color is very pale, but not quite white. It does have pink skin and light colored eyes. These horses would also have no black markings. This color does not occur in some breeds, therefore nor does the palomino color. The photo is from Wikimedia.
A chestnut horse is CC, a Palomino horse is C ccr, a Cremello is ccr ccr. As you can see a chestut can only throw chestnut genes, a cremello can only throw cremello genes, but a palomino has a fifty fifty chance of throwing either. Thus if you bred a chestnut to a chestnut, you would always get a chestnut. If you bred a cremello to a cremello, you would always get a cremello, however if you bred to palominos together, you will not always get a palomino. Let us look at what the combinations would be.
In this chart we show one Palomino parents genes across the top, C ccr, the other parents genes are on the side, C ccr, we carry all forward and down into the boxes and have the resulting combinations. We see one in four will be a chestnut, two in four will be palomino, and one in for will be a cremello. If we wanted to make more charts we could see that breeding a chestnut and cremello will always result in a palomino, and breeding a chestnut to a palomino will give a 50% chance at a chestnut and a 50% chance at a palomino. Because palomino horses do not breed true, they cannot be considered a breed.
The Halflinger is a breed of horse that "appears" to be a palomino, but in fact they are dark chestnut horses with flaxen manes and tails. Every horse in this breed has the same color, some slightly darker than others. But for sure they are all chestnuts. Since they breed true, they are not palominos.
This is a Halflinger
Remember there are more than one combination of genes responsible for color, of you have read my link on grey and roan, you will also know that this horse is therefore "CC gg RR", which means it is Chestnut, non-grey, and non-roan. They can only give a CgR genes to their off spring, those being Chestnut, not grey, not Roan. There are still more genes involved though. This photo is from Wikimedia
