Printer Friendly
Send this page to a friend
INBREEDING AND DIVERSITY - PART 1
by Fred Lanting
Copyright July, 2007 -
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 <mr.gsd@netscape.com> 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.
Figure 1. A Simple Pedigree
Bob |
Sire |
Sire |
Dam |
||
Dam |
Sire |
|
Dam |
This pedigree says that Jack and Annie are the sire and dam of Bob. When Bob was conceived, half of his chromosomal complement was paternal in origin, and half was maternal. If you then sample one of Bob's genes at random, the probability that it is identical to one of Jack's genes is 50%, or 0.5. If we extend that sample to include the whole of Bob's genotype, we find that the relationship between Bob and Jack, denoted RBJ, is 0.5. Similarly, the probability that a gene drawn at random from Bob is identical to a gene drawn at random from Tom is 0.25. This line of reasoning can be extended to find the definitions of some familiar degrees of relationship (Table 1).
Table 1. Some Common Coefficients of Relationship
Relationship |
RXY |
| Parent-offspring | 0.5 |
| Full sibs (siblings) | 0.5 |
| Half sibs | 0.25 |
| Grandparent-grandchild | 0.25 |
| Great grandparent-grandchild | 0.125 |
(Full sibs share both parents; half sibs share only a single parent.)
Equations have been developed for determining the relationships between any two related individuals, and may be found in a text on basic animal breeding. In the simplest case, the relationship between two individuals that are only related through a single line of descent is (½)n, where n is the number of steps between the two in the pedigree. For example, there is a single step between parent and offspring, so RXY = (½)1 = ½. In the case of half-sibs, there are two steps in the pedigree: one from the first offspring to the common parent and one from the common parent to the second offspring. This gives us RXY = (½)2 = ¼. This method was used to obtain the coefficients of relationship in Table 1. When inbreeding is involved, the resulting equations are very tedious to work with. A simple method that is suitable for small pedigrees will be presented later in the piece.
« Previous Page 1 2 3 Next Page » | Single page version
Fred Lanting is an internationally respected show judge, approved by many registries as an all-breed judge, has judged numerous countries’ Sieger Shows and Landesgruppen events, and has many years experience with SV. He presents seminars and consults worldwide on such topics as Gait-&-Structure, HD and Other Orthopedic Disorders, Anatomy, Training Techniques, and The GSD. He conducts annual non-profit sightseeing tours of Europe, centered on the Sieger Show (biggest breed show in the world) and BSP.
All Things Canine -- consulting division, Willow Wood Services Phone: 256-498-3319 Fax: 256-498-3311 E-mail mr.gsd@netscape.com
Canine HD and Other Orthopedic Disorders by Fred Lanting.
It covers all joints plus many bone disorders and includes
genetics, diagnostic methods, treatment options, and the role that environment
plays. This new "Hip Dysplasia and Other
Canine Orthopedic Disorders" book is a comprehensive (nearly 600
pages!), amply illustrated, annotated, monumental work that is suitable as a
coffee-table book, reference work for breeders and vets, and a study adjunct for
veterinary students, for the dog trainer
and the general dog owner of any breed.
The Total German Shepherd Dog by Fred Lanting
This is the expanded and enlarged second edition, a "must" for
every true GSD lover. It is an excellent alternative to the "genetic history" by
Willis, but less technical and therefore suitable for the novice, yet very
detailed to be indispensable for the reputable GSD breeder. Chapters include:
History and Origins, Modern Bloodlines, The Standard, Anatomy, The German
Shepherd in Motion, Shows, Showing, and Training, The Winners, Nutrition and
Feeding, General Care and Information, Health and First Aid, Parasites and
Immunity, Diseases and Disorders, The Geriatric German Shepherd, Breeding,
Basics of Genetics, Reproduction, Whelping, The First Three Weeks, Four to
Twelve Weeks, Trouble-shooting Guide.Click here to purchase
books by Fred Lanting
