GETTING WHAT YOU WANT FROM YOUR BREEDING PROGRAM
"It's accomplished by understanding whose genes
are most influential, and how to secure them."
by Jerold S. Bell, DVM
(This article first appeared in "Pure Bred Dogs/The American Kennel Club
Gazette" in September 1992. Reprinted by RCI Software with permission of Dr.
Bell.)
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
As dog breeders, we all engage in genetic "experiments" each time we produce
a litter of pups. To some breeders, determining which traits will appear in
the offspring of a mating is like rolling the dice - a combination of luck
and chance. For others, producing certain traits involves more skill than
luck - the result of careful study and planning. In order to understand (1)
how we manipulate genes within our breeding stock to produce the kinds of
dogs we want and (2) why it's important for our breeding programs to do so,
we have to first understand dogs as a species, then dogs as genetic
individuals.
The species, Canis familiaris, includes all breeds of domestic dogs.
Although we can argue that there is little similarity between a Chihuahua
and a Saint Bernard, or that established breeds are separate entities among
themselves, they all are genetically the same species. Therefore, while a
mating within a breed may be considered an outcross, it still must be viewed
as part of the whole genetic picture: a mating within an isolated, closely
related, interbred population. When evaluating your breeding program,
remember that most traits you're seeking cannot be changed, fixed or created
in a single generation. The more information you can obtain on how certain
traits have been transmitted by your dog's ancestors, the better you can
prioritize your breeding goals.
IT'S ALL IN THE GENES
Tens of thousands of genes interact to produce a single dog. All genes are
inherited in pairs, one pair from the father and one from the mother. If the
pair of inherited genes from both parents is identical, the pair is called
homozygous. If the genes in the pair are not alike, the pair is called
heterozygous. Fortunately, the gene pairs that make a dog a dog and not a
cat are always homozygous. Similarly, the gene pairs that make a certain
breed always breed true are also homozygous. Therefore, a large proportion
of homozygous non-variable pairs - those that give a breed its specific
standard - exist within each breed. It is the variable gene pairs, like
those that control color, size and angulation, that produce variations
within a breed.
What genetic manipulations have occurred to create the different breeds?
Each breed was developed by close breeding and inbreeding among a small
group of founding canine ancestors, either through a long period of genetic
selection or by intensely inbreeding a smaller number of generations. The
process established the breed's characteristics and made the dogs in it
breed true. Breeding closely related individuals increases the chance that
identical genes from a common ancestor will be passed down both the sire's
and the dam's sides of the pedigree.
BREEDING BY GENOTYPE
Such genetic manipulation is called inbreeding (and its less intense form,
linebreeding). Inbreeding creates greater homozygosity in the offspring and
fixes desirable traits. it also allows for greater expression of recessive
genes that are not expressed in the heterozygous state. If a recessive gene
(a) is rare in the population, it will almost always be masked by a dominant
gene (A). Through inbreeding, a rare recessive gene (a) can be passed from a
heterozygous (Aa) common ancestor through both the sire and dam, creating a
homozygous recessive (aa) offspring. Unfortunately, undesirable recessive
genes can also become fixed through inbreeding. However, inbreeding does not
create undesirable genes, it simply increases the expression of those that
are already present in a heterozygous state. A tendency toward disorders
controlled by multiple genes, such as hip dysplasia and congenital heart
anomalies, can be exacerbated by inbreeding.
Geneticists' and breeders' definitions of inbreeding vary. A geneticist
views inbreeding as a measurable number (called the "inbreeding coefficient"
or Wright's coefficient) that goes up whenever there is a common ancestor
between the sire's and dam's sides of the pedigree; a breeder considers
inbreeding to be close inbreeding, such as father-to-daughter or
brother-to-sister matings. A common ancestor, even in the eighth generation,
will increase the measurable amount of inbreeding in the pedigree. (The
process of calculating coefficients is too complex to present here. Lists of
inbreeding coefficients based on different types of matings are indicated in
Table 1 for general reference. Several books that include how to compute
coefficients are indicated at the end of this article; some computerized
canine pedigree programs also compute coefficients.)
The inbreeding coefficient is an estimation of the percent of all the
variable gene pairs that are homozygous due to inheritance from common
ancestors. It can also be viewed as the average chance that any one gene
pair is homozygous due to inheritance from a common ancestor.
To visualize some of the concepts in this article, please refer to Pedigree
1, the pedigree of Gordon Setter "Laurel Hill Braxfield Bilye". Notice that
the paternal grandsire, CH Loch Adair Foxfire, and the maternal grandam,
CH Loch Adair Firefly, W.D., are full siblings, making this a first-cousin
mating. As indicated in Table 1, this relationship contributes 6.25 percent
to the pedigree's inbreeding coefficient.
For the calculated inbreeding coefficient of a pedigree to be accurate, it
must be tabulated from a number of generations. This is because inbreeding
in the fifth and later generations (background inbreeding) often has a
profound effect on the genetic makeup of the offspring represented by the
pedigree.
In studies conducted on dog breeds, the difference in inbreeding
coefficients based on four- versus eight-generation pedigrees varied
immensely: A four-generation pedigree containing 28 unique ancestors for
30 positions in the pedigree could generate a low inbreeding coefficient,
while eight generations of the same pedigree, which contained 212 unique
ancestors out of 510 possible positions, would have had a considerably
higher inbreeding coefficient.
Knowledge of the depth of the pedigree may alter how you view it: What
seemed like an outcrossed mix of genes in a couple of generations will
appear as a linebred concentration of genes from influential ancestors in
extended generations.
Look again at the sample pedigree (Pedigree 1). An inbreeding coefficient
based on four generations computes to 7.81 percent. This is not
significantly increased from the estimate of 6.25 percent based on the
first-cousin mating alone. Inbreeding coefficients based on increasing
numbers of generations are as follows: five generations, 9.86 percent; six
generations, 16.64 percent; seven generations, 20.38 percent; and eight
generations, 23.22 percent. Based on eight generations, there are only 106
unique ancestors for 510 possible positions in the pedigree. The inbreeding
coefficient of 23.22 percent is close to what you would find in a parent-to-
offspring mating. As you can see, the background inbreeding has far more
influence on the total inbreeding coefficient than the first-cousin mating,
which only appears to be its strongest influence.
In order to determine whether a particular mating is an outcross or
inbreeding relative to your breed, you must determine the breed's average
inbreeding coefficient. The average inbreeding coefficient of a breed will
vary depending on the breed's popularity or the age of its breeding
population.
Rare or recently introduced breeds usually have an inherently higher average
inbreeding coefficient. (They have a limited number of potential breeding
stock available to breed to; thus they share more common ancestors.)
Popular, more established breeds usually have a lower average inbreeding
coefficient because they have access to a wide availability of relatively
non-related breeding stock.
A mating with an inbreeding coefficient of 10 percent, based on an
eight-generation pedigree, would be considered moderate inbreeding for a
Labrador Retriever (a popular breed with a low average inbreeding
coefficient), but would be considered an outcross for an Irish Water Spaniel
(a rare breed with a higher average inbreeding coefficient).
The average inbreeding coefficient for Gordon Setter pedigrees, based on an
eight-generation pedigree, is 16.36 percent. Therefore, our sample pedigree
(Pedigree 1) is relatively inbred compared to the average for the breed.
Knowledge of the degree of inbreeding in a pedigree does not necessarily
help you unless you know whose genes are being concentrated. The
relationship coefficient measures the relatedness between an ancestor and
the individual represented by the pedigree. A relationship coefficient
estimates the probable percentage of genes passed down from a common
ancestor. We know that a parent passes on an average of 50 percent of its
genes, while a grandparent passes on 25 percent, a great-grandparent 12.5
percent, and so on. For every time the ancestor appears in the pedigree, its
percentage of passed-on genes can be added up and its "percentage of blood"
estimated. The right-hand column in Table 1 shows the percentage of blood
for ancestors of different types of matings.
The relationship coefficient will vary from the percentage of blood due to
differences in the inbreeding coefficients between the ancestor and the
pedigree as a whole. For example, if the ancestor has a higher inbreeding
coefficient (and, therefore, greater homozygosity), then a single gene
passed from a homozygous pair will always represent the ancestor.
Breeders have a greater chance of reproducing an ancestor through
linebeeding, and the relationship coefficient will be higher than the
percentage of blood. If the ancestor is relatively outcrossed (and,
therefore, has a greater heterozygosity), then a single gene from a
heterozygous pair of the ancestor's will only represent 50 percent of the
types of genes available to its offspring. Such a dog's descendants will
have fewer total genes that will be the same as those of the ancestor. Its
relationship coefficient will reflect this by being lower than its
percentage of blood.
In the sample pedigree, the common great-grandparents, CH Sutherland
Gallant and CH Sutherland Lass of Shambray, have a percentage of blood of
25 percent based on their being the parents of both CH Loch Adair Foxfire
and CH Loch Adair Firefly, W.D. Referring to a pedigree analysis of the
sample pedigree (Table 2), their relationship coefficients are higher than
the percentage of blood. This is because both of their own inbreeding
coefficients were higher than that of the sample pedigree. Through greater
homozygosity, they are able to pass on a greater percentage of their total
genes to their descendants.
Increasing an individual's homozygosity through linebreeding may not,
however, reproduce an outcrossed ancestor. If an ancestor is outcrossed and
generally heterozygous (Aa), increasing homozygosity will produce more AA
and aa. The way to reproduce an outcrossed ancestor is to mate two
individuals that mimic the appearance and pedigree of the ancestor's
parents.
It is better for linebred ancestors to appear on both the sire's and the
dam's sides of the pedigree. That way their genes have a better chance of
pairing back up in the resultant pups. Genes from common ancestors have a
greater chance of expression when paired with each other than when paired
with genes from other individuals, which may mask or alter their effects.
To reproduce or concentrate the genes of an ancestor, you should use a
number of its offspring in the pedigree that share the ancestor's best
traits. If an ancestor appears a number of times in a pedigree, but always
behind the same offspring, you are only concentrating the approximately 50
percent of the genes passed from the ancestor to the single offspring: You
are linebreeding on the offspring and not the ancestor. A common example of
linebreeding is to have an ancestor as a triple or quadruple great-
grandparent, with each appearance out of a different offspring. In many
breeds, an influential individual may not appear until later generations,
but then will appear so many times that it necessarily contributes a large
proportion of genes to the pedigree. In our sample pedigree, CH Afternod
Drambuie has the highest relationship coefficient of all of the linebred
ancestors. His genetic contribution to the pedigree is second only to the
parents'. He doesn't appear in the pedigree until the sixth generation, but
then appears 33 times between the sixth and eighth generations. His dam,
CH Afternod Sue, appears 45 times between the seventh and eighth
generations, and contributes almost as much of the genes to the pedigree as
a grandparent. This again shows that the _depth_ of the pedigree is very
important in estimating the genetic makeup of an individual.
BREEDING BY PHENOTYPE
Many breeders plan matings solely on the appearance (phenotype) of a dog and
not on its pedigree or the relatedness of the prospective parents. Matings
based on appearance are called "assortative matings". There are positive
assortative matings (like-to-like) and negative assortative matings
(like-to-unlike) for individual traits. Breeders use positive assortative
matings when they wish to fix traits, and negative assortative matings when
they wish to correct traits or bring in traits the breeding stock may lack.
Some individuals may share desirable characteristics, but they inherit them
differently. This is especially true of polygenetic traits, such as ear set,
bite or length of forearm. Breeding two phenotypically similar but
geno-typically unrelated dogs together would not necessarily reproduce these
traits.
Conversely, each individual with the same pedigree will not necessarily look
or breed alike. Therefore, breedings should not be planned solely on the
basis of the pedigree or appearance alone. Matings should be based on a
combination of appearance and ancestry. If you are trying to fix a certain
trait - like topline - and it is one you can observe in the parents and the
linebred ancestors of two related dogs, then you can be more confident that
you will attain your goal.
If a linebreeding produces a puppy with magnificent qualities, but those
qualities are not present in any of the ancestors the pup has been linebred
on, then the dog may have a wonderful show career, but it may not breed
true. Therefore, careful selection of mates is important, but careful
selection of puppies from the resultant litter is also important to fulfill
your genetic goals.
OUTCROSSING
Outcrossing (matings with a lower inbreeding coefficient than the average
for the breed) tends to increase heterozygosity, matching pairs of unrelated
genes from different ancestors. Most outcrossing tends to produce
non-uniform litters. The exception would be if the parents are so dissimilar
that they create a uniformity of heterozygosity. This is what usually occurs
in a mismating of two breeds. The resultant litter tends to be uniform, but
demonstrates "half-way points" between the dissimilar traits of the parents.
Such litters may be phenotypically uniform, but will rarely breed true due
to the mix of dissimilar genes.
Outcrossing can be a useful tool to bring in traits that you do not have in
your breeding stock. While the parents may be genotypically dissimilar, you
should choose a mate that corrects your dog's faults but phenotypically
complements your dog's good traits.
It is not unusual to produce an excellent quality dog from an outcrossed
litter. The abundance of genetic variability can place all the right pieces
in one individual. Many top-winning show dogs are outcrosses. Consequently,
however, they may have low inbreeding coefficients and may lack the ability
to uniformly pass on their good traits to their offspring. After breeding an
outcross, breeders should breed back to their original stock to increase
homozygosity and attempt to fix newly acquired traits.
PUTTING IT ALL TOGETHER
Decisions to linebreed, inbreed or outcross should be made based on the
knowledge of an individual dog's traits and those of it's ancestors.
Inbreeding will quickly identify the good - and bad - recessive genes the
parents share in the offspring. Unless you have prior knowledge of what the
pups of milder linebreedings on the common ancestors were like, you may be
exposing your puppies (and puppy buyers) to extraordinary risk of genetic
defects.
As a geneticist, I am a proponent of linebreeding and occasional,
prudent inbreeding. To breed dogs for more than one or two generations,
type has to be established. In your matings, the inbreeding coefficient
should only increase because you are specifically linebreeding (increasing
the relationship coefficient) to selected ancestors.
If your breeding program is stagnating after several outcrosses, there is
really no concrete direction you can go with it. You will have an abundance
of heterozygosity, little uniformity and a diminished response to selection.
Conversely, if you run into trouble with a linebreeding program, you can
always outcross in one generation, which will bring in new genes and allow
you to immediately change direction toward more specific goals.
Don't set too many goals in each generation, or your selective pressure for
each goal will necessarily become weaker. Genetically complex or dominant
traits should be addressed early in a long-range breeding plan, as they may
take several generations to fix. Traits with major dominant genes become
fixed more slowly, as the heterozygous (Aa) individuals in a breed will not
be readily differentiated from the homozygous-dominant (AA) individuals.
Desirable recessive traits can be fixed in one generation because
individuals that show such characteristics are homozygous for the recessive
genes. Dogs that breed true for numerous matings and generations should be
preferentially selected for breeding stock. This prepotency is due to
homozygosity of dominant (AA) and recessive (aa) genes.
Trying to develop your breeding program scientifically can be an arduous,
but rewarding, endeavor. By taking the time to understand why you wish to
linebreed on selected ancestors, you can then concentrate on those
particular traits and produce a better dog. =(^v^)=
============================================================================
PEDIGREE 1: Pedigree of Gordon Setter LAUREL HILL BRAXFIELD BILYE *
1 2 3 4 5
Dual CH Loch Adair Monarch
CH Sutherland MacDuff
| CH Sutherland Dunnideer Waltz
CH Sutherland Gallant
| | CH Afternod Kyle of Sutherland
| CH Sutherland Pavane
| CH Sutherland Xenia
CH Loch Adair Foxfire
| | Afternod Fidemac
| | CH Loch Adair Peer of Sutherland, CD
| | | CH Wee Laurie Adair
| CH Sutherland Lass of Shambray
| | CH Afternod Callant
| CH Afternod Karma
| CH Afternod Amber
CH Braxfield Andrew of Aberdeen
| | Afternod Fidemac
| | Am.Cn.CH Afternod Scot of Blackbay, CD
| | | CH Afternod Alder
| | Am.Cn.CH Forecast Trade Winds, CD
| | | | Bud O'Field Brookview
| | | CH Oak Lynn's Bonnie Bridget
| | | Borderland Taupie
| CH Afternod Ember VI, CD
| | CH Afternod Simon
| | Afternod Profile of Sark
| | | CH Afternod Heiress of Sark
| CH Afternod Ember V
| | CH Afternod Callant
| CH Afternod Maud MacKenzie
| CH Afternod Amber
LAUREL HILL BRAXFIELD BILYE
| CH Afternod Callant
| Dual CH Loch Adair Monarch
| | Loch Adair Diana of Redchico
| CH Sutherland MacDuff
| | | CH Afternod Anagram
| | CH Sutherland Dunnideer Waltz
| | CH Hi-Laway's Calopin
| CH Kendelee Pendragon
| | | CH Afternod Callant
| | | CH Wee Jock Adair, CD
| | | | Loch Adair Diana of Redchico
| | CH Afternod Nighean Kendelee
| | | CH Afternod Simon
| | CH Afternod Wendee
| | Afternod Dee of Aberdeen
CH Halcyon Belle-Amie
| Dual CH Loch Adair Monarch
| CH Sutherland MacDuff
| | CH Sutherland Dunnideer Waltz
| CH Sutherland Gallant
| | | CH Afternod Kyle of Sutherland
| | CH Sutherland Pavane
| | CH Sutherland Xenia
CH Loch Adair Firefly, WD
| Afternod Fidemac
| CH Loch Adair Peer of Sutherland, CD
| | CH Wee Laurie Adair
CH Sutherland Lass of Shambray
| CH Afternod Callant
CH Afternod Karma
CH Afternod Amber
*Eight-year-old spayed female owned by Dr. Jerold and Mrs. Candice Bell,
and co-bred by Mary Poos and Laura Bedford.
============================================================================
TABLE 1: Coefficients for Sample Matings
Type of Inbreeding Percentage of Blood
Mating Coefficient to Listed Ancestor
--------------------------------------------------------------------------
Parent x Offspring 25.00% Parent 75.0%
Full Brother x Sister 25.00% Common Grandparent 50.0%
Father x Granddaughter 12.50% Father 62.5%
Half-Brother x Half-Sister 12.50% Common Grandparent 50.0%
Uncle x Niece 12.50% Common Grandparent 37.5%
First-Cousin Mating 6.25% Common GreatGrandparent 25.0%
============================================================================
TABLE 2: Pedigree Analysis for LAUREL HILL BRAXFIELD BILYE
(Based on an eight-generation pedigree)
Coefficient of Inbreeding: 23.22%
1st Generation
Linebred Relationship of appearance # times in
Ancestors Coefficients in pedigree pedigree
---------------------------------------------------------------------------
CH Afternod Drambuie 32.09% 6 33
CH Afternod Gallant 26.54% 5 13
CH Sutherland Gallant 25.49% 3 2
CH Sutherland MacDuff 25.07% 3 3
CH Sutherland Lass of Shambray 25.05% 3 2
CH Afternod Sue 23.78% 7 45
Loch Adair Diana of Redchico 17.63% 5 12
CH Afternod Buchanon 17.34% 7 35
CH Afternod Hickory 14.67% 6 24
CH Afternod Woodbine 14.03% 6 15
Afternod Fidemac 13.01% 5 7
CH Afternod Amber 12.62% 5 5
CH Afternod Kate 9.37% 6 12
CH Wee Jock Adair, C.D. 9.33% 4 3
CH Hi-Laway's Calopin 8.73% 5 5
Afternod Ember of Gordon Hill 8.53% 8 23
Afternod Hedemac 8.07% 7 15
Afternod Hedera 7.79% 7 19
CH Wilson's Corrie, C.D. 7.70% 7 16
CH Page's MacDonegal II 7.60% 7 19
CH Afternod Anagram 7.60% 5 4
============================================================================
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Dr. Bell is director of the Clinical Veterinary Genetics Course for the
Tufts University School of Veterinary Medicine and national project
administrator for numerous genetic disease control programs of pure-bred
dogs. He performs genetic counseling through Veterinary Genetic Consulting
and practices small animal medicine in Connecticut. He and his wife breed
Gordon Setters.
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
FURTHER READING:
If you are interested in learning more about these subject, consult the
following books:
Abnormalities of Companion Animals: Analysis of Heritability. by C.W.
Foley, J.F. Lasley, and G.D. Osweiler, Iowa State University Press, Ames,
Iowa. 1979.
Genetics for Dog Breeders. by F.B. Hutt, W.H. Freeman Co, San Francisco,
California. 1979.
Veterinary Genetics. F. W. Nicholas, Clarendon Press, Oxford England. 1987.
Genetics for Dog Breeders. R. Robinson, Pergamon Press, Oxford England.
1990.
Genetics of the Dog. M.B. Willis, Howell Book House, New York, New York.
1989.
COMPUTER SOFTWARE:
Dr. Bell uses a program called "CompuPed" by RCI Software, 1117 Redwood Dr,
Loveland, CO 80538, to facilitate his genetic research work.
NetPetMagazine Home Page
Dog Breed Index
For great articles! -- NetPetMagazine Table of
Contents
Support NetPetMagazine!
Products and Services