The Pit Bull Bible Online APBT Database

Wright’s Inbreeding Coefficient

The Wright’s Inbreeding Coefficient (WIC) is a mathematic calculation designed to help you understand how “tight” your breeding is (or is not) genetically. It is a feature that is found in most expensive pedigree software products, but you no longer have to buy these products because we offer it here in our database. (No other database offers this!) Further, the WIC (and all genetic calculations) become more and more valuable the deeper and deeper you go into the pedigree, and few software products go back 15-generations like our database does, and no other database goes as far back as ours does either.

The Wright’s Inbreeding Coefficient can best be defined as “the probability that both genes of a pair in an individual are identical by descent,” i.e., homozygous (the same). In other words a WIC of 20% means that a given dog has a 20% likelihood of having the identical genes as his parents. This probability must be viewed as a “probabilily,” not a certainty. The genes your dog actually get, in the real world, might be totally different from this computer-projected “probability.”

This calculated inbreeding coefficient is simply a function of the number (and location) of the common ancestors in a pedigree. It is not a function, except indirectly, of the inbreeding of the parents, per se, but of the relatedness of the whole background. Thus, one can mate two highly inbred individuals who share little common ancestry with each other and produce a litter with a very low Inbreeding Coefficient. (An example of this would be Diablo Rojo, whose parents are both highly-inbred individuals themselves, but who are nonetheless totally unrelated to each other. Thus Diablo Rojo is almost a 100% straight outcross and thus his WIC is virtualy 0.00%.)

Conversely, it is possible to mate two dogs who, though not directly off of common parents, share a such similar genetic background in their ancestry, that (although both of the individuals themselves have low Inbreeding Coefficients), combining them together in a mating boosts the Inbreeding Coefficient of their pups substantially. An example of this would be Thunder. His sire Poncho had a 14.03% W.I.C. ... and his mother Red Sonja had a 15.99% WIC ... and neither had any common parents. But the relatedness of their entire genetic whole, when combined, boosted the WIC of Thunder above both of his parents to 22.59%. (All calculated @ 10-generations deep.)

Like many other genetic calculations, the Wright’s Inbreeding Coefficient is based on probabilities, not certainties. An individual may actually be more (or less!) highly inbred than the number computed in the formula suggests, simply by the random genetic intangibles that no program can accurately duplicate. The Wright’s Inbreeding Coefficient is to give you an idea of the relatedness of the TOTAL WHOLE of the genetic background, not a certainty. There is a difference between how “tight” a breeding is off a particular individual dog than there is as to how “tight” a breeding is in its entire genetic aggregate. The Wright’s Inbreeding Coefficient is a more encompassing view of the tightness of “the whole genetic aggregate” than it is a mere glimpse of a percentage-breeding off of “an individual dog.” To show what I mean by this, Misty Red and Space Man were both "75% Poncho dogs" ... meaning each animal was produced by Poncho being bred to one of his daughters. However, there was a 25% outcross in Misty Red’s background, and so her Wright’s Inbreeding Coefficient was only 48.71%. By contrast, Space Man was a 100% linebred individual, across the board, so his Wright’s Inbreeding Coefficient was a much-higher 59.06%. Yet each dog was a product of a father/daughter Poncho breeding.

Thus the depth of value of the Wright’s Inbreeding Coefficient can be seen in its best light, as it encompasses more than just the tightness of a breeding on an “individual dog” (in this example, Poncho), but instead the Wright’s Inbreeding Coefficient focuses on the tightness of the GENETIC WHOLE.

Like any tool, the Wright’s Inbreeding Coefficient has very good practical use, but it should not be misused or misunderstood. Two dogs out of the same litter may share the same theoretical WIC “on paper” ... but IN THE REAL WORLD one dog may happen to carry with it a substantially-greater “pull” from one side of its pedigree than its littermate brother or sister. For instance, Laguna Sunrise and Jezebel were littermates out of the same litter of Poncho to Screamer. Therefore, “on paper” these two sisters have “an identical” WIC. However, the physical reality is Laguna Sunrise carries a much greater “Hollingsworth” (or even Red Baby) GENETIC PULL AND EXPRESSION than did her sister Jezebel, who carried a much stronger “Poncho” pull in her actual physical expression and characteristics. So, again, use the Wright’s Inbreeding Coefficient as a tool, but do not be blinded by this tool; use your eyes in conjunction with it.

In closing, as a general rule, a coefficient of 10% (or less) is a scatter-bred dog (or possibly a 100% straight outcross), where there is little relatedness in common amongst the entirety of BOTH parents’ ancestries. A 10%-20% WIC is a somewhat linebred dog. Coefficients of 20%-35% are getting into some solid linebreeding in the genetic background, and anything with over a 35% WIC. is an intensely inbred/linebred animal.