 |
|
|
|
|
by Kathy Parrish Every year as spring draws near I begin to hear the familiar refrain of ‘what will I get if I cross a black and a chocolate’ or ‘what will I get if I cross a palomino and a black’. Unfortunately, the question just creates more questions that need answered to get a thorough answer. While in a perfect world color would not be a determining factor in breeding, in today’s market the color of the foal can be the difference between getting top dollar or having to just about give the foal away. As the market for horses tightens and supply increases, breeders have become increasingly interested in breeding for specific colors. In the past, the color of choice was always chocolate with a white mane and tail, but in recent years I’ve seen an increased interest in other colors. To thoroughly answer the question of what we will get when we cross two horses, I have to know not just the color of your horse but also what hidden color genes you horse might have. I usually break the task up into several parts. The first is to figure out the base coat colors (black, bay, or chestnut), then what modifier genes (silver dapple, cream, roan, grey, dun) were needed to create the colors seen in the horses. Table 1 contains the ‘color formulas’ for many of the popular colors. The table shows the base coat color and the modifier gene needed to create the color. Table 2 contains a list of the most common modifier genes as well as how the gene affects the horse’s color. The base coat color is controlled by two genes. The first determines if the horse can produce the color black on its body at all (bays and blacks) or if it will be all red (chestnuts). The scientists refer to this gene as the Extension gene so you will see it symbolized with an ‘E’ on the color DNA tests to refer to the dominant of the gene (produces black) or an ‘e’ for the recessive (red) version of the gene. The second gene determines if the black on the horse will be only on the points (bay) or over the entire horse (black). This gene is called the Agouti gene. The dominant of the gene (‘A’) produces bay and the recessive (‘a’) produces black. Table 1. Color Formulas
Once we know the base coat and modifier genes present in the horses to be bred, we then need to figure out what might be hidden. So this second step is to figure out the hidden genes for the base coat. For this we have to ignore the modifier genes, so if I talk about a black, bay or chestnut then that includes any of the colors in that column in the color formulas table. Depending on the base color of your horse, different genes can be hidden. For instance a black or bay might be carrying a recessive gene to produce chestnut. Table 2. Modifier Gene's Affect on Coat Color
If EITHER of its parents is a chestnut OR if it has EVER produced a chestnut then it must carry the recessive gene for it. A bay might also be hiding the recessive gene to produce a black as well as the recessive gene to produce chestnut. Once again if EITHER of its parents is a chestnut OR if it has EVER produced a chestnut then it must carry the recessive gene for chestnut. If EITHER of the bay horse’s parents is a black OR if it has EVER produced a black then it must carry the recessive gene for black. Because a chestnut does not have any black on its body, you can not tell looking at the horse if it will produce black or bay. If BOTH parents were black then you know that the offspring carries two genes to produce black. If ONE parent was black then you know that the offspring will carry at least one gene to produce black. In the past, if we had not owned the horse its entire life, we were unlikely to know the answer to the above questions. Now that the RMHA’s pedigree database is online, we can investigate the colors of not only your horse’s parents, but also any of their registered foals. The database can be accessed through the RMHA web site at www.rmhorse.com. In SOME cases this can answer the above questions. If you still can’t figure out what hidden genes your horse carries then there is always the option of pulling some tail hairs and sending them off to have DNA color testing done, but this gets expensive for a large herd. The alternative is to make some educated guesses based on what the ‘typical’ genetic makeup is for a Rocky Mountain Horse. Table 3 shows the current color breakdown for the Rocky Mountain Horse. The category ‘Other’ takes in all the misspellings and varieties where there is only one entry in the database. As you can see, chocolate is the most abundant color followed by black. Based on the data, it can be assumed that at least 32% of the non-chestnut herd carries the red gene since about half that number are either chestnut or palomino. Note that I said at least 32% carry the gene because I recognize that in the past many breeders did not bother to register a foal if it was a chestnut, so the number could be much higher. Bays, Buckskins and Red Chocolates make up about 18% of the non-chestnut herd. Since the bay base color is dominant, 18% of the chestnuts can be assumed to carry a bay gene (that means that 82% do not), but the 18% once again may be a little low. Table 3. Rocky Mountain Horse Herd Colors
What all this means is that if you don’t want to spend the money for color DNA testing and you still don’t know enough by looking up the parents and offspring of the horse then you can still make some educated guesses and have a good chance of being right. MOST chestnuts will carry the genes to produce black instead of bay; MOST bays will carry one gene to produce black. These are pretty sure guesses because the percentage of bay horses in the association is so low. The red gene on the other hand is present in a much higher percentage of horses. If you have a bay or black base coat color horse, neither parent was chestnut and the horse has not produced a chestnut, then the most accurate way of predicting if the horse carries the red gene is to look up the other offspring of the horse’s parents in the online database. If EITHER parent EVER produced a foal with a chestnut base coat color (chestnut, sorrel or palomino) then you have a 50/50 chance of the horse in question carrying the red gene. If BOTH parents had produced chestnut base coat colored offspring then the odds go up to 67% that your horse will carry the red gene. If neither parent is shown to have produced any chestnut offspring then assume until proven otherwise that the horse in question does not carry the red gene. The last information that needs to be figured out is the hidden modifier genes. The most common of these would be the silver dapple gene. As can be seen on Table 2, the silver dapple gene does not affect the color red on a horse, so any of the chestnut base coat colors will hide this gene. If the horse has EVER produced a chocolate or red chocolate when bred to a black or bay horse then you know that the horse carries the silver dapple gene. If NEITHER of the parents of the horse were chocolate, red chocolate, chestnut, or palomino then your chestnut horse can not carry silver dapple (for instance the chestnut offspring of breeding two blacks). If neither of these tests give you an answer then you should assume that your chestnut carries the silver dapple gene since over 60% of the RMHA herd appears to carry the gene. The one other modifier gene that could be hidden is the cream gene on a black based color. Fewer then 10% of the herd appears to carry the cream gene, so assume that that they don’t carry it unless they have produced a palomino or buckskin when bred to a bay or chestnut. It is a commonly known fact that the foundation stallion, Maple’s Squirrel, did carry the cream gene, so his direct offspring have a 50/50 chance of carrying the cream gene if they are chocolate or black. Now that you know not just the color of the horses you plan to breed, but what hidden genes they carry, go to Table 4. Because of space considerations, I could not list all possible breeding combinations. Across the top I listed what appears to be some of the more common colors found in the association. Down the side I listed both the more common colors and several not so common. Table 4. Expected Outcome of Typical Breeding Crosses
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
