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Basic Genetics...Article: Basic GeneticsAuthor: MindiBown Kennels Almost everyone, whether they're involved in breeding of any kind or not, is familiar with the terms Dominant & Recessive. The easy trap to fall into here is to believe that ALL genetics is of a dominant / recessive nature. Sorry to disillusion you but that is not the case. However, this simple type of genetic structure is a good place to start in our studies. To illustrate our point, let's take a classic example which is also pertinent to our breed. The Genetics of Long vs Smooth Coat ChihuahuasAll genetic studies should start with the simple explanation that each gene, regardless of what it controls is basically made up of two parts. These parts are referred to as alleles. We inherit one allele from our mother and one from our father. The two alleles, when combined form a single gene. That gene may be the one that controls the colour of our eyes, or perhaps the colour of our hair. In the case we are looking at here, they control whether the dog will have a smooth or a long coat.To begin, let's first of all understand that at this level of genetic study we will assume that there are only two possible alternatives to a particular trait. In this case, long or smooth. Next, Let's accept that there are only 2 alleles in each gene. Now that I've said that, I must point out that this is NOT the case in every instance. Size for instance is made up of 6 alleles. 3 from each parent. Colours may have 4 or 5 or even more possibilities, (or alleles) to choose from. But for now let's be happy with the simple version. Ok, there are two possibilities. Long or smooth. In the case of Chihuahuas, smooth is dominant. What does this mean? Quite simply, if a pup inherits a smooth coat allele from either parent, it WILL be a smooth. Even if one parent is a long. Look at it this way:
Now what would happen if we bred Dog 1 with Dog 2? Remember, each parent contributes one allele to their offspring. Logically they can only give what they've got.2 possibilities from 2 parents means there are 22 = 4 combinations possible.
The thing to remember here is that if you are looking at a bitch or stud dog. If that dog is a smooth, but has a long coat parent, he or she is like the pups above. They can throw a long coat pup. (Given the right partner) Now, let's try a more interesting combination with less predictable results. How about 2 like dog 3?
Pup 1 is a long. That's obvious. Pups 2 & 3 are smoothes, but carry a long coat allele. Pup 4 is a smooth. So out of 4 pups, 3 are smoothes. According to the laws of genetics, this is so. HOWEVER! We also have to deal with the laws of probability or chance. Toss a coin into the air and what are the chances of it coming up heads? Right....50/50 Toss that same coin into the air 10 times. Will it come up heads 5 times? Maybe, maybe not. So far this is primary school stuff. Now, if you toss that same coin in the air 10 times and it comes up heads every time, what are the odds of it coming up heads on the 11th toss? Answer? 50/50 !....Don't agree? That's what makes two-up such a deadly way to lose money! Dogs are the same. You combine the genetics of two dogs that SHOULD give you what you are looking for, and then sit back and wait to see if the coin comes up heads, and you get what you want, or tails, and someone gets themselves a new pet Chihuahua. Now here's one for you to figure out. If we put two like dog 1 (Long/Long) together, what would we get? I'm not going to slow the loading of this page down any more by putting in another diagram. This one is easy. Each parent can only pass on what they've got. A long coat dog has only long coat alleles to give therefore every single pup will be a long. PERIOD! Do you know there are breeders who will insist that they've had a smooth from a double long breeding? Genetically speaking, it is impossible. Now, before assuming that a breeder who makes this claim is therefore dishonest, let me say there are 3 possibilities. 1. The (most obvious) A smooth coat dog got somewhere he shouldn't have. This is probably the explanation in 9 out of 10 cases. However there are 2 more possibilities 2. The pup is actually a long coat, but with such a terrible coat that it resembles a smooth or 3. The pup is the result of a mutation. This third option is a distinct possibility, although the odds against it are enormous. A similar situation exists in the Saluki breed. There are 8 documented and DNA confirmed cases in the USA in the past 20 years. By understanding the genetics involved, you may begin to understand one of the reasons a smooth/smooth is so valuable to us. What this means to a breeder is that every single pup a smooth/smooth produces WILL be a smooth. There is just no other possibility. This predictability is of great value to us. One effective way of improving a long coat is to bury the long coat gene (allele) for a generation. A smooth/smooth will do that. Put a male smooth/smooth to a long coat female and you can only end up with Long/Smooth pups. The pup itself will of course be a smooth. But in the next generation if we put that Long/Smooth pup to a Long/Long partner, we will have the long coat back, hopefully better than before. That's the theory anyway. In practice of course, it's a toss of the coin. I guess in the long run, breeding has and always will be just like tossing a coin. A sound knowledge of genetics however, can at least insure that you aren't using a double headed coin. (C)Copyright 2007, this article is copyright protected Special thanks to MindiBown Kennels for permission to display this article on RoyaltyChi Chihuahuas website |
