It is estimated that nearly 70 percent of the world is lactose intolerant to some extent.¹ This means that nearly 70 percent of individuals are unable or have difficulty digesting milk and milk products. In humans, the lactase phlorizin-hydrolase (LCT) gene allows for lactase production, an enzyme that helps to digest lactose.² Yet, lactose intolerance plagues certain populations more than others.

Recent studies have looked more specifically into lactose persistence in certain populations. A 2002 study identified two SNPs in the lactase gene that segregate at a high frequency in lactase persistent individuals of European descent.⁵ A SNP or single-nucleotide polymorphism is a substitution of a single nucleotide in the genome. The SNPs were found in the MCM6 gene. The SNPs were studien in both European and African populations; when a detailed genotype-phenotype study was conducted on 470 Africans they found three new variant SNPs. In short, they determined that lactase persistence in european and African populations was convergent evolution, a process in which organisms independently evolve similarly in response to similar selective pressure.

In this lab we strive to emulate this study, attempting to determine the lactose intolerance of various individuals using their DNA. To extract DNA from each individual, cheek cells were swabbed with a toothpick. The toothpick was then submerged in a DPX buffer which was optimized for cheek cell DNA extraction. After the DNA was incubated it was time to set up a Polymerase chain reaction (PCR). PCR is ametid used to rapidly make (amplify) millions of copies of a DNA sample, allowing for the DNA to be studied.³ To set up the PCR the forward and reverse primers were diluted and then added to the DNA as well as mole grade water.

A process called gel electrophoresis was used to separate DNA according to their size. The DNA was placed into a charged box where the molecules were subsequently separated by the electrical field through a gel with small pores.⁴ Gel electrophoresis was used to determine which DNA samples could subsequently be sequenced. The acceptable DNA samples were sent to a lab to be sequenced and returned to us, where we were able to analyze them using Benchling.

After analyzing the sequenced DNA we were able to determine whether or not individuals had SNPS correlated to lactase persistence. We looked at two SNPs in particular. The first was G/C-140.10 SNP, originating in African populations where a G represents lactose intolerance. The second was C/T-13910 SNP, originating in European populations where T represents lactose tolerance. Finally, we determined whether they were homozygous or heterozygous for lactose tolerance or intolerance where T is dominant in heterozygous individuals with the European SNP and G is dominant in heterozygous individuals with the African SNP.⁶

The evolutionary benefits of lactase persistence are still unclear, but what is known is that not only is this an instance of convolution, but more specifically gene culture coevolution.⁷ In this way we see that science and culture have a vital role to play to compliment one another. There is no way we can fully understand our biological evolution without also investigating our cultural evolution.