Date of Completion


Degree Type

Honors Thesis - Campus Access


Biology (BIOL)

First Advisor

Kam D. 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 more than 25 single nucleotide polymorphisms (SNPs) are found in this enhancer region, though approximately five are most closely associated with lactase persistence. The best-studied is a C->T variant (rs4988235) at position -13,910 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 heterogeneous US population. This research seeks to fill this gap. I summarize previously published SNP data as well as genotyping data gathered in the Dahlquist lab at LMU. A more reliable estimate of the frequency of LP and LNP in the US population will allow us to shape US dietary guidelines so that they reflect the needs of diverse groups.