Using a Case Study Article on Earwax to Enhance Understanding and Interest in Genetics.

The next time your students clean their ears, they might be tempted to examine their earwax and have a better appreciation for genetics. For four consecutive semesters, students in an Introductory Biology class at Coastal Carolina University were assigned to read a case study article that explores the link between a single gene and earwax type. The case study article, broadly defined as a story with an education message (Herreid, 2007), was originally published by the New York Times (Wade, 2006) and summarizes original research performed by Yoshiura et al. (2006). Briefly, the case study article explains that humans either have wet or dry earwax and continues by highlighting that Japanese researchers have recently identified the gene that determines the type of earwax an individual is destined to have. The gene, designated ABCC11, has two different alleles. A single point mutation in the ABCC11 gene, in which an “A” for adenine substitutes “G” for guanine, will produce the dry earwax phenotype only if the person has two copies of the recessive allele. In contrast, individuals with at least one dominant “G” allele will have wet earwax. Individuals with African and European ancestry are more likely to have wet earwax, while dry earwax is most prevalent among Koreans, Japanese, and Han Chinese in northeastern Asia. The article concludes by noting a difference in opinion as to why the dry earwax allele is still persistent in the human population. The researchers correctly noted that dry earwax is strongly associated with less sweating and decreased body odor, which they opine may be an adaptation to cold winters typically experienced in northeastern Asia. Other scientists have rationalized that genetic drift may simply best explain why the allele for dry earwax is still found in some Asian ethnicities and that this allele was not likely favored by natural selection as postulated by the original researchers. The case study article is assigned to students after a three-week unit covering Mendelian genetics, transcription, and translation. The article is read just prior to introducing the different types of mutations that can occur in DNA. Students are required to answer questions that pertain to the article prior to the next lecture. The case study article refrains from using common genetic terms that students have learned and previously used to solve genetic problems. Terms that are not included, but can be inferred from the case study article, include: dominant, recessive, heterozygous, homozygous, genotype, phenotype, and alleles. I take advantage of the omission of these terms and have students apply these definitions as they answer the following questions: • Are there two types of genes or alleles that determine earwax? • What phenotypes are associated with each gene variant? • Which gene variant is recessive and which is dominant? • What is the chance a child will have wet earwax if one parent has a heterozygous genotype and another parent has dry earwax? • Speculate if earwax type and body odor are influenced by nurture, nature, or both. • What’s the difference between natural selection and genetic drift? Which do you believe is more responsible for the prevalence of dry earwax among Native Americans?