The following is based on an excerpt from the 1999 edition of The Total German Shepherd Dog by Fred Lanting, and may not be reproduced without approval. © 2003. Contact the principal author at for permission to quote. Some of the following charts and calculations have been contributed by a geneticist friend, John B. Cole, Department of Animal Science, University of Minnesota.
Introduction
Jay Lush, father of modern animal breeding, stated that variation is the raw material with which breeder works. The focus of this article is on the use of variation and measures of variation, in making breeding decisions. It includes the related ideas of relationship and inbreeding, as well as systems of mating that make use of these ideas. The use of crossbreeding to introduce genetic variation into small populations will also be explained. Our goal is to provide some practical tools for genetic management and decision-making.
Most breeders keep records (pedigrees) of their animals and their animals’ performance. Information such as litter size, milk production, and slaughter weight are collected when such information is of importance. The more information we have, the more informed and accurate our decisions become. This chapter will show us how to use the information at our disposal to make good decisions.
As dog breeders, we are most concerned with breeding animals that typify breed standards for physical appearance, temperament, mental acuity, and similar traits.
However, in most cases we only have pedigree information and a small number of recorded traits on which to base our decisions. While scientists now understand the genetic basis for moderately complex traits such as coat color and pattern, research in other species suggests that there is little or no significant genetic component to such indicators of performance as success in the show ring, The dog breeder, then, is often at a loss for accurate s ources of information about performance traits he is interested in. We shall show how to make the most of what is available.
Relationship
When animals are related ‘by blood’, as the expression goes, they share a proportion of their genes in common. It is assumed that the genes shared in common between two related individuals have descended from the same ancestor. If that is true, the genes are termed identical by descent (IBD). That is, genes shared by two related individuals are identical because they have the same origin. Genes may also be what is termed identical in state, which means that the genes at a locus are identical in form, but did not descend from the same ancestor. The coefficient of relationship between two individuals X and Y, RXY, is a measure of pedigree relationship, and may be thought of as either
- the expected proportion of genes that are IBD between X and Y or
- the correlation between the genotypes of X and Y based only on pedigree relationship.
The probability that genes are IBD for two individuals provides the basis for our numerical measure of relationship. We will develop the idea with an example that refers to the pedigree in Figure 1.