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Complex Traits

Author(s): Nancy Moreno, PhD.

Understanding Long Hair in Dogs

Procedure (cont.)

7. Have students work in teams of two or four persons, and give each group a copy of the student sheet, “Understanding Long Hair in Dogs.” (Refer back to slide 19 to remind students of SNPs if they have questions.) Have students read the instructions on the student sheet carefully (see bulleted list below), and work to find the location of the change in the genetic code that correlates to long vs. short hair. Students will examine the sequence data to find the location (row) with a pattern of nucleotides that best matches the phenotypes of the individuals (long vs. short hair).

Complete instructions from the student sheet.

  • The following table presents sequence data from a gene that controls hair growth in dogs. The gene is found on dog chromosome number 32, and contains about 70,000 nucleotides (or “letters”). Certain sections of the gene appeared to be more variable, and those sections were sequenced in ten individual dogs of different breeds. The investigators found a number of locations where individual dogs had different nucleotides at the same spot along the DNA strand. These locations are given in the table below.
  • The columns in the table represent the 10 sampled dogs. Each row corresponds to a single location where the nucleotides (letters) were different. Biologists refer to a mutation at a single nucleotide position as a SNP, pronounced “snip” (which stands for single nucleotide polymorphism). Many times, these tiny mutations do not cause any differences between individuals. Remember that each dog has two versions of the nucleotide (one on each chromosome). 
  • Your challenge is to find the SNP location that explains the differences between the dogs that were sequenced. In other words, which SNP location best matches the pattern of long vs. short hair?

8. You may need to guide students with questions, such as, Which rows do not show any changes from one individual to the next? Can you eliminate these rows from further consideration? Why or why not? [The rows may be eliminated because they do not help discriminate between the short- and long-haired dogs.]

Remind students, to think about patterns within each pair of nucleotides, because each individual has two copies at every location. When the two nucleotides are the same within a pair, the condition is called homozygous. When the two nucleotides in a pair are different, the condition is called heterozygous.

9. Have each team present its results and the rationale for the selected location, or write a paragraph describing their findings. [Students will find that only one row (location 20) completely matches the pattern of long vs. short hair. Dogs with two copies of the T nucleotide at this location exhibit long hair.]

10. Discuss students’ findings in class. Help them to understand that the single substitution of a “T” for a “G” led to the formation of a defective protein, which in turn, altered the signal for telling individual hairs to stop growing. In other words, the mutation causes a loss of function in hair growth regulation, presumably leading to longer hair. Only dogs with two copies of the mutation have long hair. It is likely that dogs with one copy of the short-hair allele produce enough of the hair termination protein to keep the hair from growing excessively. 

Funded by the following grant(s)

Science Education Partnership Award, NIH

Gene U: Inquiry-based Genomics Learning Experiences for Teachers and Students
Grant Number: 5R25OD011134

Robert Wood Johnson Foundation

Using Learning Technology to Build Human Capital
Grant Number: 57363