Without a working knowledge of the genetics of producing a better Siberian, the breeder is limited to combining dogs together that seem to physically complement each other when genetically the mixture may be unsound. At the very least, in order to avoid certain genetic faults, an understanding of recessive, dominant, homozygous, heterozygous, variable penetrance,line breeding, in breeding, polygenic recessive, etc. needs to be understood, if not becoming fully second nature. It is the goal of this and following articles to familiarize readers with genetic terminology and to instruct the Siberian fancier on those traits that have proven modes of inheritance. Even if certain patterns of inheritance are not known, a knowledge of genetics can only assist a dedicated Siberian fancier who wishes to responsibly contribute back to the breed by producing a litter of puppies. Why know about genetics? I heard recently about two breeders being uncertain as to what color the puppies out of 2 red Siberians would be. Most of you know that 2 reds Siberians will produce red puppies, or possibly a red piebald or a red splash coat but that you can't get black and whites or greys if both parents are red. (As a twist that will be explained later, you could also get whites with liver points.) But did you know that the reason the breeding of 2 reds results in red offspring is because reds are homozygous for the autosomally recessive red factor? Knowledge like this helps breeders determine or control both trivial qualities (like coat color) in the breedings that we plan and more importantly, the cornerstone qualities like temperament, angulation, back length, foot shape, tail set and carriage, etc. Genetics as a science was not understood until the monk, Gregor Mendel, made some insightful observations with peas around the year 1900. Serendipitously, pea genetics are very straight forward and intuition allowed an understanding of simple recessive and dominant traits. From this work, the field of genetics began. Much was understood about breeding good animals before Mendel discovered the "wheel", but new concepts were able to be developed and old wives' tales discarded once the concept of recessive traits were accepted. For instance, colors that were thought to result from genetic "weakness" resulting from inbreeding like the fawn and blue color in Dobermans and the red in Siberians could now be understood as a combination of recessives rather than a loss of "strong" outcross traits. All traits are carried or coded for on alleles. Alleles are the building blocks of genes. Therefore all traits are carried on a gene or a combination of genes. Genes are bodies of DNA that are made up of many alleles each specifying certain proteins that determine the trait(s) in question. Genes (and the alleles that make them up) are inherited on chromosomes (each chromosome consisting of many genes) that are donated from the mother (egg or ovum) and father (sperm). The dog has 78 chromosomes arranged in 39 pairs, one of which determines the animal's sex (though other traits are also carried on the sex chromosomes). One chromosome of each pair of chromosomes comes from the mother and the other chromosome of the pair comes from the father. There are always 2 alleles that code for the same trait (e.g. 2 alleles that code for coat color). These alleles are arranged within genes on each of two chromosomes that make up one of the 39 pairs. One (allele, gene, and chromosome) is inherited from the mother and one from the father. Now we can take a diversion from precise terminology, since the difference between alleles, genes, and chromosomes is understood, and use the term allele and gene almost interchangeably. Since multiple alleles exist in a given gene, it is customary to refer to a "gene coding for a certain trait" rather than "an allele on a gene coding for a certain trait." You need to understand the difference between alleles and genes for later understandings in genetics but the customary use of the word gene is often not as precise as it should be--don't be confused by this. To continue with the discussion, while there are 2 genes (actually alleles) that code for the same trait, they are not necessarily identical (e.g. one may code for a red coat and the other may code for a black coat). This is where the terms recessive and dominant become operational. If one gene is dominant (e.g. black) and the other is recessive (e.g. red) then the end product (e.g. the dog's coat color) will be revealed as the dominant trait (e.g. black) and the recessive gene will be silently held to possibly reveal itself in subsequent generations. Therefore dominant genes for physically apparent traits are always revealed in the animal's physical appearance (phenotype) whereas recessive genes may or may not be revealed, depending on whether the gene it is paired with is dominant or also recessive. Phenotype is the expression of a combination of genes. Genotype is the actual genetic make up of the individual. In the example above if the animal's "coat color genes" are both red, then the animal will be red (red phenotype-- the genotype is homozygous red) because there is no dominant gene to hide the red gene's expression of coat color. Now if we take the example of two red parents, both having two recessive red genes, the offspring, receiving one gene for coat color from each parent, can only receive red recessive genes (since the parents cannot carry the black color gene or they wouldn't be red) and hence all the offspring will be red. The inheritance of coat color is different from the inheritance of coat color distribution though, so other genes will determine if the red coat color will be distributed as a splash coat, piebald, white (restriction of pigment from the hair shaft) or irish (i.e. solid on the top and white underneath and on the legs), as is the most common color distribution in Siberians. More on that and more terminology in the next installment. The building blocks in this column are extremely basic and there are exceptions to the general principles outlined here that I will attempt to detail later. Despite the exceptions, learn these terms cold to begin to understand the genetics of breeding a better Siberian Lessons in this column: Dominant: a trait, that when present on a gene in a single dose, will mask the presence of another. It is usually depicted by upper case letters (e.g. B for black). Recessive: a trait that needs to be present in duplicate in order to indicate its presence. In a single dose it will be masked by a dominant gene. It is usually depicted by a lower case letter (e.g. r for red). Thus the B for black combined with a r for red would be depicted Br, which would code for a black coat color. Chromosome: gene carrying body in a cell, there are 39 pairs, or 78 total, in dogs. Gene: building block of chromosomes made up of DNA. Allele: building block of genes made up of DNA. Autosome: any chromosome other than the sex chromosomes. There are 38 pairs of autosomes and 1 pair of sex chromosomes that make up the 39 total pairs of a dog's chromosomes. An autosomal trait is one that is carried in a gene on an autosome. A sex linked trait is one that is carried in a gene on one of the sex chromosomes (almost always the X, rather than the Y chromosome). Phenotype: The visible expression of traits. Genotype: The actual genetic structure. Homozygous: both copies of a trait on a gene are identical. Heterozygous: copies of a trait on a gene are different.
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