Inbreeding: Not A Taboo Subject

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In a recent St Fancier, there was a letter to the editor about an article I had written on the stud dog, Cronus. I made reference to the fact that Cronus had Titan closely behind both his sire and his dam.  The writer took issue with any notion that Cronus was "inbred" saying:

"By definition Cronus was not inbred. At most one could state Cronus was doubled up on Titan. Inbreeding is the mating of father/daughter, mother/son, or siblings."

I find this confusing. How can he be "doubled up" but at the same time "not inbred"? And just how does one define inbreeding anyway? By the writer's definition, the matings of first cousins or grandchildren back to grandparents, for example, would not be considered "inbreeding".

The writer is entitled to whatever definition of inbreeding he likes, but that does not mean the scientific world agrees with him. If one seeks out a definition from universities and vet schools internationally, one finds the following:

Technically, the COI is the probability that both genes of a pair in a dog are identical.  Simply put, it's a measurement of inbreeding. 

It is calculated by a mathematical formula that is somewhat complicated to many users.  The function is...

COI = sum[ (.5 ^ (a + b + 1)) * (1 + c) ]

a = Generations between sire and common ancestor
b = Generations between dam and common ancestor
c = COI of common ancestor

When breeding, one is either concentrating genes (inbreeding) or not (outcrossing). It is only a matter of the degree to which inbreeding occurs. A father-daughter mating results in a COI of 25;  cousins only 6.5;  distant relatives, maybe only 1. No common ancestors, i.e., outcrossing, a COI of 0. If a common ancestor does not show up on both the top and bottom halves of a pedigree, it will not impact the COI of the dog.  

Whenever inbreeding is mentioned there is a tendency to treat it as a taboo subject. Inbreeding must be bad, we say. But linebreeding is good, right? This, of course, is nonsense. Linebreeding is nothing more or less than a watered down form of inbreeding. We convince ourselves that a COI of under 5 is somehow better than a COI of 12.5 or higher. Why do we do this?

I suppose it is because whenever we hear the word "inbred" we are conditioned to think of very damaged genetic specimens and hear the tune "dueling banjos".   Our societies and our religions all warn against "inbreeding". And with good reason: inbreeding can go too far and the results can be horrific. When this happens with animals or plants, the failures can be culled and weeded out of the gene pool. We can't/shouldn't do this with humans. Hence the taboo.

However, we ARE dog breeders. Dog breeders must manage genes. The question isn't how high or low the COI is in itself. The question is: are we concentrating the right genes? If you "double up" on bad genes you run the risk of getting very poor specimens. Conversely, if you "double up" or inbreed using good genes, you increase the chances of getting superior specimens of a certain type. 

St Bernards look like St Bernards because of selective breeding over hundreds of generations. Certain genes were concentrated. Certain lines breed true to a specific look because of genetic concentration. 

Inbreeding, to whatever degree, is an essential component of every form of life alive today. So every breeder must accept it, study it, and use it wisely.

Our favorite inbred example? Yondo, with a COI of 17%.