An explanation of coat inheritance in Chihuahuas published in the June-July, 2003 issue of Los Chihuahuas
John E. Cipollina
Hartsville, South Carolina (843) 332-2313
Fax: (843) 332 1521
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The interbreeding of coats in Chihuahuas comes up as a topic of discussion quite frequently. Some people come out in favor of it, others do not. I have been interbreeding coats since I started breeding and have had no adverse side effects in my breeding program because of it. I have read some of the concerns of those who are against it and I would like to take this opportunity to address those issues.
As many of you already know, I teach at a Middle School. Each year, the science department invites me to bring in my dogs and give a seminar on the practical application of genetics in a breeding program. With the Chihuahuas and the Chinese Crested Dogs, I use coat inheritance as an example of dominant and recessive traits. I will explain it as I do to the 7th grade science classes.
All traits are inherited from the parents. The genes determine those traits. Each parent contributes half of the genetic material; therefore, genes come in pairs. A gene can either be dominant or recessive, the dominant trait is what we see. In Chihuahuas, the Smooth Coat is the dominant trait and the Long Coat is the recessive.
What we see is phenotype. The genetic make-up is referred to as genotype. In Chihuahuas, phenotype is either Long Coat or Smooth Coat as is Hairless and Powder Puff in the Chinese Crested. Genotype is what lies underneath.
In discussing genotype, it can go several ways. In the case of the genotype in the Smooth Coat Chihuahua, the genetic make-up can go one of two ways. Should both parents contribute the dominant gene, the phenotype will be Smooth Coat and the genotype will be referred to as homozygous. Should one parent contribute the dominant gene and the other the recessive, the phenotype is still that of a Smooth Coat but the genotype will be referred to as being heterozygous. Heterozygous can also be referred to as a hybrid. In the case of the Long Coat, the phenotype is Long Coat and the genotype is homozygous because the Long Coat is a recessive trait and must be paired with another recessive gene in order for that trait to be visible.
When cells become sperm or egg cells, the genes that are paired up in the parents split. The homozygous parents can only contribute the dominant gene if their trait is dominant and those with visible recessive traits can only contribute the recessive gene. In the case of the heterozygous or hybrid parent, they can contribute either the dominant or recessive gene.
What this translated to in the case of the Chihuahua, a Long Coat bred to a Long Coat can only produce Long Coats because it is a recessive trait. In dealing with the Smooth Coats, the genotype of the sire and dam determines the trait of the get. If a homozygous Smooth Coat is bred to a Long Coat, all of the get will be Smooth Coats in phenotype and heterozygous in genotype. The reason being, the Smooth in this case can only produce the dominant gene and the Long the recessive. When a homozygous Smooth Coat is bred to a heterozygous Smooth Coat, the get will be Smooth Coat in phenotype and can be either heterozygous or homozygous in genotype. In the case of two heterozygous Smooth Coats being bred together, the phenotype can be either Long Coat or Smooth Coat and in the case of the Smooth Coat get, they can be either homozygous or heterozygous in genotype. When a heterozygous Smooth Coat is bred to a Long Coat, the get can either be Long or Smooth but all of the Smooth Coats will be heterozygous because of the Long Coat parent. Lastly, two homozygous Smooth Coats mated can only produce Smooth Coat get in both phenotype and genotype.
With this being said, the concerns about losing our Smooth Coats by interbreeding I find to be totally unfounded. Two heterozygous Smooth Coats can produce a homozygous Smooth no matter how many Long Coats are in the pedigree. In other words, mathematically, it is highly improbable for the Smooth Coat to become extinct due to the interbreeding of coats. As far as the quality of coat goes, it has absolutely nothing to do with the fact that a Long was bred to a Smooth. I would challenge anyone to look at the coats of the dogs in my kennel and tell me the trait of the sire's and dam's coat just by looking at the dogs with no knowledge of what is in the pedigree. Another concern I wish to challenge is that the quality of one variety is poor due to the interbreeding of coats. In my opinion, this is totally absurd. There is consistency in the quality of both my Long and Smooth Coats because when I choose breeding pairs, I look at the overall quality of the dogs and consider the coat type and color last. To pass up an opportunity to make an improvement in my breeding program because of coat type would not be a sound decision.
Breeding dogs is like any other endeavor in life. To be successful, one needs to look at the entire picture before making decisions. Those who select breeding stock based on the least amount of faults are breeding to the lowest common denominator and generally will breed only mediocrity. The most successful breeders, who have consistently produced good representatives of the breed, have based their breeding decisions on the knowledge of the virtues of their breeding stock. JMO
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