This pedigree is fictitious, but it is an excellent example of both an inbred and a line-bred pedigree. In looking at the numbers we see that Fedon has Diviseur in the third generation in both the paternal and maternal side. 3 + 3=6; therefore this individual can be considered mildly " inbred." If Diviseur had appeared as a grand parent on both sides, then the combined values would equal four and the degree of inbreeding would be more acute. Then we see that Fedon has Etincelle in the third generation on the paternal side and in the fourth generation on the maternal side. 3 + 4=7, so Fedon is considered linebred to Etincelle. However, we also see he has Jonquille in the fifth generation on both sides. 5+5=10, which is greater than nine; so this pairing is considered to be too far away to have any bearing on the pedigree.

Remember, inbreeding indicates a higher degree of homozygosity. This method is good to quickly determine the general degree of inbreeding in a pedigree, but it does not give us an accurate idea of the degree of increased homozygosity that could be present in this individual. For that, you will need the next method.

In his work, Systems of Breeding, Sewell Wright developed a formula to determine the degree of homozygosity likely to be present in an inbred individual. The number, which is calculated by this formula, is called the coefficient of inbreeding. It is an estimate of the percentage of homozygous pairs above and beyond the assumed 50% for a purebred animal.

Fx=S(1/2)^a+b (1+Fa)

Wright’s Formula states that the coefficient of inbreeding is equal to the sum of one-half raised to a power equal to the number of generations from the sire to the common ancestor and back to the dam times one plus the coefficient of inbreeding, if any, of the common ancestor. In other words, if we start with the base 50%, Wrights Formula tells us what percentage we must add to that to have an accurate idea of the increased homozygosity of the individual. If an animal has a coefficient of 25% it would mean that 25% of the REMAINING 50% (or 12.5% of the total) are likely to be homozygous. So the total gene pairs that are homozygous would be 50% + 12.5% or 62.5%.

However, if you’re sane, you forgot your algebra shortly after you learned it. Fear not, there’s a slightly longer means of calculating this formula by hand that requires only addition and the use of the table below.

Each pedigree is divided into generations just as in the previous method. The parents are expressed as generation F1, the grandparents as F2, the great-grandparents as F3 et cetera. To use the above chart, simply identify the common ancestor(s) in a pedigree. For example: In the pedigree used as an example previously we find Diviseur on the paternal side in the F3 generation. We also find him on the maternal side twice in the F3 generation and once in F4. For each combination (from paternal to maternal) we must calculate the percentages and add them together (in other words, coefficients are collective). F3 + F3=3.13%
F3 + F3= 3.13%
F3 + F4=1.56%

So Diviseur has contributed 7.81% of the remaining 50% to the increased homozygosity. But we cannot stop there. We also find Irma in the F3 generation of both the sire and dam. So to our total we must add another 3.13% to make 10.94% of the remaining 50%.But wait, we need to look a little farther. We see that Etincelle is the mother of Irma. We have already calculated Irma so there is no need to calculated Etincelle, EXCEPT that Etincelle ALSO appears in a different context as the mother of Tyrolienne. This makes her a separate factor and we must now calculate for her as well. On the Paternal side, she appears in the F3 generation as the mother of Tyrolienne. On the maternal side she appears in the F4 generation as the mother of Irma.

F3 + F4 = 1.56%

Our final calculation looks like this: Diviseur 7.81% + Irma 3.13% + Etincelle 1.56%, for a grand total of 12.50% of the remaining 50% or 6.25% of the total. 50% + 6.25% =56.25% homozygous.Get it? Work through several on your own and it will begin to be clear.  The secret is to keep a sharp eye for ALL the combinations. Remember you are only looking for matches between the two sides of the pedigree; matches on the same side are irrelevant. Work backwards from the individual whose pedigree it is.  Once you find a common ancestor, there is no need to also calculate for all of his ancestors (which are also on the pedigree as many times as he is) UNLESS they appear in a different relationship.

Finally we come to Percentage of Blood. This calculation assumes that any individual is the product of the sum of its genetic makeup.n this method, all generations in the pedigree together are equal to 100%. So the parents would each contribute 50% of the total genetic material, the grandparents 25% and so on. In an inbred pedigree each incident of a given individual must be added together to give the total of his contribution to the whole. This method differs from Wright’s Formula in that the coefficient of inbreeding expresses the percentage of homozygosity (the percentage of both genes in a pair being alike) while percentage of blood only calculates the probability of one of the genes of any given pair is present in the individual, passed down from the ancestor in question.

Using the values in the following table will allow you to quickly calculate the percentage of blood for any given ancestor. When the ancestor only appears once then his contribution will be the basic value for the generation in which he appears. However, if he appears more than once, then you must add together all the values for each and every time he appears in the pedigree.