Date of Completion


Degree Type

Honors Thesis - Campus Access


Biology (BIOL)

First Advisor

Dr. Kam Dahlquist


The human trait of lactase persistence (LP) is the ability to produce the enzyme lactase, and thus digest the milk sugar, lactose, into adulthood. Reports of how many in the world’s population express this trait range from 16-35%, although this may be an overestimate. Most adults worldwide are not able to metabolize lactose effectively, referred to as lactase nonpersistence (LNP). The consumption of dairy products by an LNP individual can result in mild to severe gastrointestinal symptoms such as bloating, gas, and diarrhea. The lactase enzyme is encoded by the LCT gene on chromosome 2, whose expression is regulated by an enhancer that lies over 13,000 base pairs upstream of the transcription start site. A review of public SNP databases reveals that >25 single nucleotide polymorphisms (SNPs) are found in this enhancer region. The best-studied is a C>T variant (rs4988235) at position -13910 bp upstream, where molecular evidence shows that the T allele confers the trait of lactase persistence. Databases show frequency data for this SNP for some homogenous populations, but reliable data is not found for the heterogenous US population. Our work seeks to fill this gap. We have genotyped 21 individuals for the -13910 C>T SNP so far. 33% are CC, 62% are CT, and 5% are TT. Generally, the genotype corresponds to self-reported frequency of dairy consumption and gastrointestinal symptoms. A more reliable estimate of the frequency of LP and LNP in the U.S. population will allow us to shape U.S. dietary guidelines so that they reflect the needs of diverse groups.