Canine Genetics and Breeding Strategies: The Basics
Part Two: Looking at Pedigrees
By Arliss Paddock
In Part One of this article (Summer 2011 AKC Breeder), we considered the genetic road map of dogs as a species and the mechanics of how the traits that determine the countless aspects of an individual dog—from the color of his coat to the way he carries his tail—are inherited from his parents.
In this issue, we look at different types of pedigrees and how they can aid in the making of breeding decisions.
The Influence of Ancestry
In the mid-1800s, Austrian monk Gregor Mendel experimented in crossbreeding thousands of pea plants in the monastery's garden. His observations and careful record-keeping of the traits of successive generations led to his formulation of the primary laws of inheritance. He published a paper about his work, but his ideas, which included description of how some traits are dominant and some recessive, were rejected at the time. Early in the 20th century, however, his research was rediscovered and his findings became the basis of the new science of genetics.
Bonnie Nance ©AKC
Long before Mendel, though, those interested in breeding animals to improve certain characteristics kept detailed records of matings and ancestry. This was an important complement to skillfully assessing an animal's apparent traits, or phenotype. Evidence shows that drawn pedigrees were used more than 600 years ago in the breeding of livestock.
Whether breeders were focused on dogs, horses, pigs, or other animals, they recognized the value of knowing the parentage of potential breeding stock and the strengths or weaknesses of an animal's ancestors.
The Traditional Pedigree
The word pedigree comes from the French phrase pied de grue, or "crane's foot" – which a traditional pedigree diagram, with its divergent branches representing several generations of parents and offspring, resembles. This type of pedigree is the most popular of those used by breeders, and it is valuable as a historical record and in identifying and analyzing the extended ancestry of individual dogs.
Pedigrees can, however, take a number of other forms as well. Breeder, researcher, AKC judge and board member, and noted canine authority Dr. Carmen Battaglia, who lectures around the world about dog breeding and canine genetics, presents extensive information about several alternate types of pedigree and their usefulness to breeders in his "Breeding Better Dogs" program (breedingbetterdogs.com).
Regarding the traditional type of pedigree, Battaglia notes several disadvantages to its use:
"Unfortunately, the traditional pedigree, as a breeding tool, has many shortcomings. Most notable is the importance it places on memory and on knowing the names and titles of the ancestors ... The custom has been for breeders to recognize and associate names and titles with what could be remembered about the traits and characteristics of each ancestor. This approach lacked reliability, and it did not capture the information needed to plan a breeding. ... Perhaps its major criticism was that it did not lend itself to collecting the right kinds of information in sufficient detail to be useful to plan a breeding. A review of how most traditional pedigrees are used shows that scribbled notes around the edges and in the margins typically serve as the record system. Notes such as 'beautiful coat,' 'wonderful type,' a title, or the name of a famous offspring become the information a breeder has to use. This approach fails to collect what is relevant or specific to making improvements. In short, breeders have no way to learn from their mistakes."
Although traditional pedigrees of course provide certain important information, ideally the breeder also makes use of other types of pedigrees and additional tools when researching breeding decisions.
Other Types of Pedigrees
Three other pedigree types of value to the breeder are the visual or photo pedigree, the prism or stick-dog color-chart pedigree, and the symbols pedigree. Each has particular strengths and applications, and all three have strongly visual components.
Glossary of genetic terms
A good starting place in learning how traits are passed along through breeding is to have a basic familiarity with some important terms and concepts.
• The Visual or Photo Pedigree —
The visual pedigree or photo pedigree is a traditional-format pedigree (usually three-generation) that includes prominent photos of every individual. Numerous examples of this type of pedigree can be located online by searching on the terms "visual pedigree" or "photo pedigree." An example is found at stonehavenmastiff.com/sax_ped.htm, which presents an excellent photo pedigree of a Mastiff.
The photo pedigree can provide a useful record of the overall breed type of the dogs featured and their phenotype in terms of some specific traits such as color, ear carriage, head shape, and so on. Also, it can allow one to assess how strongly (or not) certain physical traits seem to carry through from a given individual to succeeding generations.
Like traditional pedigrees, however, photo pedigrees offer incomplete information. For example, they don't provide any clues about temperament or movement, and they typically include minimal health data, if any. However, with the increasing ease of shooting digital photos and video and uploading media to the Internet, it is likely that many online pedigrees soon will not only include photos but clips of the dogs in motion. And as the availability of genetic testing and health certifications for a wide range of conditions continues to increase exponentially for all breeds, pedigrees of all kinds are likely to include more and more extensive health information over time.
All of this is good news for the responsible breeder who seeks to make the best-informed breeding decisions possible.
• The Prism or Stick-Dog Color-Chart Pedigree —
Another very useful tool for breeders is the stick-dog color-chart pedigree, also known as the prism pedigree (with prism referring to its use of a spectrum of colors). This type of pedigree is highly recommended by Battaglia and also by Claudia Orlandi, Ph.D. Orlandi is an AKC judge and was AKC Breeder of the Year for 2009. Her Topsfield Basset Hounds, owned and bred with her late husband, Dom, have won more than 100 Bests in Show. Orlandi developed a study program for breeders, "The ABCs of Dog Breeding" (abcsofdogbreeding.com), and presents numerous educational seminars on this and other topics.
The prism pedigree is composed of stick-figure dogs positioned in pedigree format in place of the written names of the corresponding dogs. Each stick figure is made up of separate structural parts, with each part representing a trait of the actual dog. In the diagram, these parts are drawn in outline so that each may be filled in using a marker of any of four or five colors–each color indicating the degree of quality of that trait in that dog.
The prism pedigree largely focuses on the conformation traits described in the breed's standard. Traits for the real dog's separate structural parts can correspond exactly with their location on the stick figure–head, neck, front, back/topline, rear, and so on. Alternately, some parts can represent other specific traits, at the discretion of the person completing the prism pedigree. For example, the breeder may decide to color-code the tail segments to represent temperament or movement.
The specific colors used by Battaglia and Orlandi vary slightly, but generally the colors correspond with the shades of dog-show placement ribbons–with blue indicating "first place," or excellent quality based on the breed standard, followed by descending rankings of red, yellow, and white/green. (Orlandi adds a fifth color, brown, to indicate lowest quality.)
Whatever traits are represented, the color-coding of the entire group of stick figures allows patterns and trends of inherited characteristics to be seen at a glance.
Orlandi points out that a breeder may choose to focus his color-coding on traits that he specifically wants to improve in breeding. She notes:
"The breeder seeking to produce better shoulder layback, for example, should color-code the shoulder layback of each stick figure in the first three generations of the proposed breeding, basing his choice of color on how good or bad the shoulder angulation is. This provides not only a visual summary of the quality of shoulder layback, but it also gives an idea of how many, if any, well-laid-back shoulders are likely to be produced in puppies from this mating."
Battaglia gives the example of a stick-dog pedigree of a brood bitch where she, her sire, and her maternal grandparents each are shown to have a "fourth-place" (poor) front. This, he says, "suggests that she inherits her faulty front legitimately from her ancestors." Further, he explains, "It should also be noticed that poor fronts occur on both sides of her pedigree. This is useful information when searching for the right stud dog and the traits he is expected to improve."
For more information and to see examples of prism or stick-dog color-chart pedigrees, visit topsfieldbassets.com or breedingbetterdogs.com.
• The Symbols Pedigree —
Whereas the prism or stick-dog color-chart pedigree is most useful in revealing inheritance patterns of an array of conformation traits, the strength of the symbols pedigree is in demonstrating trends in the occurrence of a few specific traits. It is particularly useful for tracking the incidence of health conditions. In fact, this type of pedigree is widely used by researchers studying diseases in a variety of species, including humans.
An important aspect of the symbols pedigree is that it includes all offspring from each pairing shown, rather than simply representing the direct line of descent of one individual, as a traditional pedigree does. Because of this, its format can be described as broad or horizontal rather than vertical.
In displaying information about all littermates that result from the pairing of a dog and bitch, the symbols pedigree can more accurately reveal the family's overall genetic status with regard to certain traits or conditions. It can clarify the genetic makeup of the individuals in the family tree and shed light on how a certain trait is inherited.
This type of pedigree is so named because it employs standardized symbols representing the gender, genetic status, and relationship of individuals in the depicted family.
For example, a hollow square represents an unaffected male; a filled-in square, an affected male; a hollow circle, an unaffected female; a filled-in circle, an affected female; and so on. Horizontal lines connecting two symbols represent a pairing, and a vertical line connecting these to other symbols represents offspring. Successive generations are labeled with Roman numerals. Color-coding can provide additional information.
"The symbols pedigree is a powerful tool because of the amount of information that can be coded and quickly recognized," Battaglia notes. "Breeders ... can use several colors to code this pedigree. Keywords and phrases can be added to clarify and further explain characteristics, conditions, and test results for each ancestor, and the repetition of a color, keyword, or phrase usually signals that a genetic trend or pattern may be present."
Putting It All Together
Pedigree research is an important part of the responsible breeder's decision-making process, and we are fortunate today to have excellent tools and methods available to help in this.
In the next issue, we will conclude the series with a look at utilizing these tools and a basic understanding of genetics in the development of sound, effective breeding strategies.
Arliss Paddock breeds and shows English Cocker Spaniels and is former managing editor of the AKC Gazette.
References and further study
Battaglia, Carmen. Breeding Better Dogs, BEI Publications, Atlanta, 1986.
Bell, Jerold S., DVM. "The Ins and Outs of Pedigree Analysis, Genetic Diversity, and Genetic Disease Control." siriusdog.com/bell-pedigree-analysis-genetic-diversity
Willis, Malcolm B. Genetics of the Dog. Howell Book House, 1989.