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INBREEDING AND DIVERSITY - PART 1

by Fred Lanting

Copyright January, 2009 -

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 sources 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

1. the expected proportion of genes that are IBD between X and Y or
2. 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.

Figure 1.   A Simple Pedigree

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

(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.

Inbreeding and Relationship

The idea of inbreeding is closely tied to that of relationship. Inbreeding may be simply defined as the mating of individuals more closely related than the population average. Another definition often used is that the parents of an inbred individual shared a common ancestor. In Figure 2, Horatio is the product of a sire-dam mating: his dam and paternal grand-dam are one and the same; Emma is the common ancestor.  It is hoped that the lovely Emma is exceptional in some character that would warrant her use in this manner, rather than simply a victim of circumstance. The mating of close relatives such as seen here is sometimes called close inbreeding. Since more of an individual’s genes come from the same source, in a sense the gene pool is getting shallower. More formally, homozygosity increases in a population that is inbreeding.

Figure 2.   A pedigree demonstrating inbreeding

Inbreeding is a double-edged sword: it has both beneficial and detrimental effects.  The most useful feature of inbreeding is an effect called prepotency, which is the ability of an individual to produce offspring whose performance is very much like their own. Inbred individuals are homozygous at more loci than the population average, and they produce fewer types of gametes, resulting in fewer types of zygote at fertilization. For example, inbred and non-inbred individuals may have the following genotypes:

The inbred individual can only produce two types of gamete: ABc or Abc. The non-inbred individual, on the other hand, can produce eight different gametes (ABC, ABc, AbC, Abc, aBC, aBc, abC and abc). Prepotency is particularly useful if a parent is homozygous for a dominant allele, which each offspring will receive with certainty. However, it is really only of great value if the trait is simply-inherited (under the control of a single pair of genes) or highly heritable.  When a trait is complicated in its genetic control, or the environment is much more influential than genetics, any effects of prepotency are overwhelmed.

Continued in PART 2

General info on The Sieger Show Experience with tour guide Fred Lanting 

The  SV Bundessieger-Zuchtschau (BSZS or Sieger Show) in Germany is generally held in the last week of August or first week in September at a different location each year, depending on stadiums available. (The cost of stadium for this one-weekend event, and the competition with soccer/football events that sign contracts for many per year, determine the choice.) For the past 20 years or so, I have offered my non-profit 6-7-day guided tour of the show and sightseeing, including visits to kennels and training clubs. Get an SV judge's perspective of the bloodlines and procedures, along with experienced introductions to Germany's culture and beauty. My groups come from all parts of the globe, so even just the companionship is like a world-travel experience. We usually arrive on the Wednesday or Thursday before the show, and return the following Wednesday.

Looking for a great dog-related experience combined with seeing a different part of the world? Whatever your breed or activity in dogs, the annual Lanting guided show-and-sightseeing tour could be the experience of a lifetime. Read my annual “Impressions” articles on various websites for an idea of what we've seen in recent years. Tours centered on other countries’ Sieger Shows, the BSP, and world Schutzhund trials are also available if enough people sign up.    

None of "my people" have ever been sorry, and all have wished they had done it earlier! You will see the best of the breed, meet important GSD people, sometimes see another country or two, and have the over-all greatest dog show experience of your life. I also include, if you decide to join us, a variety of travel tips. I offer an SV conformation judge's perspective of the show (I also have AKC, UKC, and foreign judging experience). One year, when a travel-agency tour leader again deserted his group, they came to where my group was sitting and asked me questions. References available from previous tour participants. Testimonials are numerous. I hope you will join us and recommend this tour to your friends and acquaintances. As a judge with much experience in Schutzhund training and competition, and being very familiar with Western Europe, I am able to give the best tour possible. People going it on their own cannot see the important parts of the country (sometimes we tour adjacent countries, too), and paying for your rental car is more than chipping in to pay for the van and my expenses. Read my "Impressions" on various websites for an idea of what we've seen in recent years.

There will be 3 long days of the big show, and about 3 to 4 days of sightseeing and visits. Please let me know as soon as you can, with a $400 (US) deposit, so I can start putting my notification list together and finalize (hold) hotel reservations for you. There is a lot of work involved in putting together such a tour! I will make the hotel plans based on your deposits, & arrange the visits and van(s). Easy, fun, educational and, for most --- the unique trip of a lifetime. You will not be any younger next year, and if you don't make the decision to get out there and smell the roses NOW, while you think of it, you're more likely than not to lose the opportunity and desire.  Join the group! Tell others about it, too. Fred 

Contact me at  Mr.GSD[at]netscape.com and tell your friends and Internet contacts.
Postal mail: 3565 Parches Cove, Union Grove, AL  35175-8422 USA

Editor’s Note:  A well-respected and frequent GSD specialty and all-breed judge for many clubs around the world, with KC and other-country credentials, Mr. Lanting since 1966 has lectured on Gait-and-Structure, Canine Orthopedic Disorders, and other topics, and has judged in about 30 countries, including the prestigious FCI Asian Shows hosted by Japan Kennel Club and the KC of India, the Scottish Kennel Club, and many National Specialties in the USA and elsewhere. He has been described by a former OFA director as the world’s leading non-veterinarian authority on hip dysplasia. A dog breeder since 1945, a GSD owner since 1947, and a show judge since 1979, he has lectured at numerous veterinary schools in the USA and abroad. He is the author of “must read” books for the dog owner (see below for ordering info).  Curriculum Vitae available upon request.

Announcing the new “Canine HD and Other Orthopedics Disorders” book: The expanded revision is a comprehensive (nearly 600-page), amply illustrated, annotated, monumental work that is suitable as a coffee-table book, a reference work for breeders and veterinarians, and a study adjunct for veterinary students. It is equally valuable for the owner of any breed. It covers every aspect of HD and other orthopedic, bone, or spinal disorders, and includes genetics, diagnostic methods, treatment options, and the role of environment. Your autographed copy will be mailed from the USA as soon as the appropriate amount is received and is processed. Pricing: US $68, plus $5 postage in the U.S., or ask about mail overseas. Combine orders with “The Total German Shepherd Dog” by the same author ($50 plus postage). 17 of the 20 chapters are suitable for owners of any breed.