BioEd Online

Teacher Background

As described in the previous activity, all dogs are members of the same species (Canis familiaris). Even though members of different dog breeds vary physically and even behave in different ways, all domestic dogs can interbreed and produce viable offspring. The variation among (i.e., “between”) dog breeds is the result of selective breeding over time. In many cases, distinctive traits of a particular breed is the result of the crosses between close relatives. Unfortunately, inbreeding also will consolidate undesirable traits, such as hereditary diseases. Thus, breeders and owners have considerable interest in knowing about the genetic makeup of their dogs. Breeders, for example, would like to avoid breeding dogs that can pass on genetic diseases, such as von Willebrand’s disease (an inherited bleeding disorder), to their offspring.

Several companies now provide genetic tests for many disease-causing mutations and common physical characteristics, such as coat color. In addition, genetic testing can provide insights into the ancestry of mixed breed dogs. This information is useful to owners, who would like to know if their dog has hidden disease tendencies or has ancestors with specific behaviors (such as herding or barking).

Genetic testing does not examine the entire genome of an individual. Instead, it looks for irregularities in the chromosomes themselves, changes in specific sections of DNA or even proteins that are associated with a specific trait or disease. The dog genome is divided into 78 chromosomes, with 38 pairs of non-sex chromosomes and a pair of sex chromosomes. Sex in dogs in determined the same way as in humans: females have two “X” chromosomes (one from each parent) and males have one “X” and one “Y” chromosome. The DNA is chromosomes stays in a tightly wound or bunched state, until a section is “unwound,” to enable the DNA to be read.

In this activity, students will learn how one family used genetic testing to uncover the ancestry of an unusual puppy. In addition, they will examine the relationships among common clusters of dog breeds, and investigate the characteristics of different breeds.

Objectives and Standards

Materials and Setup

• PowerPoint^® slide set that accompanies this unit (Complex Traits Image Set)

• Computer and projector, or interactive whiteboard

• Copies of student page, "Dog Breeds Diagram" (one per student or one per group)

Procedure and Extensions

1. Play the NPR radio story, Hounded by Doubt, Dogged Owners Probe a Mystery, which may be found at the link below. Or download the transcript and have students read the story. Photographs of Dovekie and a purebred golden retriever are provided on Slide 11.
   
   http://www.npr.org/templates/story/story.php?storyId=127484075

2. Encourage a discussion by asking questions, Have you heard about genetic testing before? What does genetic testing examine? Do you think they will be able to figure out who Dovekie’s parents are? Tell students that genetic tests can be developed to identify unique hereditary information, and that genetic information often is used to understand relationships among different families or groups. Remind students that most organisms (including humans and dogs) have two sets of genetic information, with a single set coming from each of the individual’s two parents. This information is carried on DNA molecules (students will learn more about this process in Activity Three).

3. Display the accompanying Slide 12 of a litter of puppies and their parent (or print copies of the slide for students to share). Ask students, What do you observe about the puppies in this photograph? Students should notice that several different coat colors and patterns of markings are present. In addition, none of the puppies has the same markings as the mother. Ask, Where did this variation come from? Invite student responses—they should identify the parents (through genetic information, genes, DNA etc.) as the sources of the observed variations in the puppies.

4. Next, show Slide 13, which shows several different dog breeds. Ask students to identify the ways in which the different kinds of dogs differ in appearance [body size and shape; head shape; coat length, color and curliness]. Tell students that modern dogs provide an interesting model for learning genetics, because humans selected desirable dogs to breed—based on the parent dogs’ appearance or behaviors. This process over many generations, and many crosses, led to the different kinds of dog breeds.

5. Have students work in teams of two, and give each team a copy of the “Dog Breed Diagram” (Slide 14). Tell students that the diagram represents the complex genetic relationships among different dog breeds and was developed using information similar to that used for genetic tests ordered for Dovekie. Clarify for students that the circular diagram was created from a linear branching diagram like the one in the previous activity.

   Have students answer the following questions. Discuss as a group.
   
   • What is the closest ancestor to dogs? [Wolves]
   
   • How many major clusters of dog breeds have been identified? [10]
   
   • What is the closest branch to the retriever group? [Newfoundland]
   
   • Why are Mastiff-like dogs shown in several different branches of the tree. [They contain genetic similarities to several other groups, probably because of crosses between groups.]
   
   • Which breed clusters might be represented in Dovekie based on his appearance?

6. Play the radio story, The Case of the Mystery Puppy Solved! (Sort Of). The story can be found at the link below. Tell students that they should be prepared to discuss the following questions after listening to the story. Alternatively, you may download and print the transcript and have student read the story, The Case of the Mysterious Puppy, Solved! (Sort Of).
   
   http://www.npr.org/templates/story/story.php?storyId=127563468

7. Have students work in groups to answer the following questions (Slide 15). Afterward, conduct a class discussion about the story and guiding questions.
   
   • What did his owners learn about Dovekie?
   
   • What kind of dog is Dovekie?
   
   • What does this story tell us about the commercial applications of genetic testing?
   
   Dovekie is a mixed breed dog with an unusual appearance. After genetic testing by three different companies, his owners learned that he had a mix of genetic material from a rare breed (purebred wirehaired pointed griffon) and almost purebred golden retriever , or golden retriever mix. The somewhat different results from each lab demonstrate that genetic testing techniques still are being refined, and that results, while informative, may need interpretation.

8. To conclude, have each team of students select a dog breed from the diagram, and use resources on the website of the American Kennel Club (www.akc.org) to learn more about their assigned or selected breed. Each team should prepare a written description of the origin, original purpose, physical characteristics and unique attributes of their selected breed. Have students report their findings during the next class period.

Handouts and Downloads