More_about_breeding

Each generation of ancestors in a pedigree contributes 100% of the genes for the target animal (proband). Therefore, the percentage of contribution from each ancestor at a given generational level is 100 divided by the number of ancestors in that generation. Since the number of ancestors doubles in each preceding generation, the contribution from each ancestor in each preceding generation is halved.

However, this is not like mixing paint! Percentage of blood for ancestors beyond the parents is probabilities, not certainties. When a male passes on one set of his chromosomes, they will include a random selection of the genes he inherited from both of his parents, but there is no guarantee that the genes he passes on will contain an equal amount from each of his parents and in fact, it rarely is. There is even a small chance (very small) that he will pass on those genes from only one of his parents. On the other hand, the more times that an ancestor appears in a pedigree behind different offspring, the more likely it will be that the percentage of genes passed down from each of its parents will be closer to 50%. By the time we get back 10 generations, the contribution from each of the 1024 ancestors would, in theory, amount to slightly less than 0.1%. However, in the pedigree of the average purebred dog, there are seldom more than 100-200 different (unique) ancestors and some may appear 50 times or more. These significant ancestors make the major genetic contributions. If you have a pedigree, you can calculate % contribution of any repeats simply by multiplying the number of times each ancestor appears in any generation by the appropriate percentage for that generation and then add together all of the calculated percentage of contributions from each generation. The table listed below shows the percentage of blood inherited from each ancestor at the given generation levels. Generation "1" is the parents.

Databases exist for many breeds that will contain the data enabling you to extend a pedigree to 10 generations or more. Manual computation, though tedious, is still possible, but hardly convenient. However, the CompuPed pedigree program will quickly calculate % contribution for selected ancestors or all ancestors for a specified number of generations, providing you with information on which dogs have been most influential.

The formula for the RC is:

RAB = 2fAB ÷ [(1 + FA)(1 + FB)]½

Where fAB is the inbreeding coefficient of a hypothetical litter between A and B, and FA and FB are the inbreeding coefficients for the two individuals, A and B. A simpler approach to the breeder's problem would be to compute the RCs for C vs D and E, and D vs E. This is not an easy pencil and paper calculation. However, presented with just such a problem, it took me about 2 minutes to obtain the three RCs with the latest version of CompuPed. My results were RCCD = 10.4%, RCCE = 13.4%, RCDE = 17.2%. D and E share the most common ancestry, while C and D share the least, and respectively so would the progeny from their two prospective litters. To minimize inbreeding and maximize diversity, all else being equal, C and D would be the best choice. (These values actually all fall below the average for the breed, which is about 23 %.) The Kinship Coefficient The fAB term in the RC equation is sometimes called the "kinship coefficient" and may be used as a measure of the relationship between two individuals. Its computation is the same as that of an inbreeding coefficient for a hypothetical litter between the two dogs. (It does not matter if they are the same sex.) The mean kinship (mki) for individual i is is the average of the kinship coefficients (fij) between i and all the other breedable individuals in the population: A conservation biologist would consider the individual with the lowest mean kinship to be the most genetically valuable in terms of maintaining diversity in the population, and would try to favor that individual in a breeding program.