Analysis of a SNP linked to lactase persistence: An exercise for teaching molecular biology techniques to undergraduates.

Recent experimental evidence indicates that the ability of adults to tolerate milk, cheese, and other lactose-containing dairy products is an autosomal dominant trait that co-evolved with dairy farming in Central Europe about 7,500 years ago. Among persons of European descent, this trait is strongly associated with a C to T substitution at a polymorphic site 13,910 bp upstream of the lactase gene. This mutation results in the persistent expression of lactase into adulthood enabling individuals carrying a T(-13,910) allele to digest lactose as adults. In this report, we describe a laboratory exercise for an undergraduate molecular biology course in which students determine their own genotype at the -13,910 polymorphic site and correlate this with their ability to tolerate dairy products. The exercise is used as a tool to teach basic molecular biology procedures such as agarose gel electrophoresis, PCR(1), and DNA sequencing. Students are actively engaged in the learning process, not only by analyzing their own DNA but also by applying their knowledge and skills to answer an authentic question. The exercise is also integrated with lecture material on the control of gene expression at the transcriptional level, in particular, how transcription factors can influence the activity of a promoter by binding to cis-acting DNA regulatory elements located within the proximal promoter of a gene or distant enhancer regions.