Got Lactase?

Elizabeth Ghil and Riya Gupta

What is Lactose Intolorance?

Lactose intolerance is when your small intestine cannot make enough lactase to digest it.

Lactase enzyme -->


The reason many of us are lactose intolerant is because when we grow into adults, our lactase protein making gene gets switched off. When we were babies, lactase acted as a lactose scissors, cutting lactose in half and allowing us to digest it.

When scientists tried to figure out the history of lactose intolerance, they found that in our European ancestors fossils that there was no lactase in their bodies, indicating that we have evolved/mutated into a lactose tolerant species. Lactose tolerance is only advantageous to communities with domesticated dairy producing animals.

Natural selection favored those with the lactase making gene, spreading it through nearly the entire population. Countries such as Africa led parallel lives to those in Europe. They also herded domesticated dairy producing animals. African populations began to herd, lactose tolerance became an advantageous trait. Researches then later found that the mutation of this gene had occurred and started to spread. Lactose intolerance was born. This had also occurred in Europe due to the fact that they raised and herded cattle the same way. Even though these countries were far away, cultural traditions caused evolution even among distance and ethnic boundaries.

Researchers found mutations with matching DNA samples that always had the lactase gene turned on to see if something was lactose intolerant. To prove that mutations were advantageous , the team had looked for evidence of a selective sweep. The rapid spread of a mutation that is advantageous would spread at the same time to the new mutation. The quicker the sweep, the less the combination can be broken up.

Mechanisms of Evolution: Mutation

Mutation is applied to this concept of lactase being turned on and off because lactase tolerance and intolerance is a mutation

Question 1

Are you lactose tolerant or lactose intolerant? Based on the information in this article, explain how your genes affect your ability (or lack of ability) to digest milk.

Riya and I aren't lactose intolerant, but that's because even when we were growing into young adults, our bodies still produced a lactase making enzyme.

Question 2

Read about the concepts of genotype and phenotype. Explain how these concepts apply to a lactose tolerant individual.

If a lactose tolerant gene is a dominant gene, then that would be the genotype for a lactose tolerant individual. The lactose tolerance is the phenotype because it's the physical trait for the genotype of a lactose tolerant gene. Lactose tolerance can spread through a population that is based on domestic farming of milk. When populations start to herd then lactose tolerance becomes an advantageous trait. This mutation is favored by natural selection of a population that depends on dairy.

Question 3

Review some background information on natural selection. explain how a lactose tolerance mutation would spread through a human population that herds of cattle. Make sure to include the concepts of variation, selection, and inheritance in your explanation.

If a group or family herds cattle, then the cattle is going to be their main source of food, because they have to keep the herd moving. So if an individual in the group is lactose intolerant, then after a while of living herding cattle, they might develop a tolerance to lactose since they have to live off of it.

Question 4

Now imagine that the population described in the question above lived during the Paleolithic before any animals were domesticated. How would that change your answer to the question above?

Even if there was a population with a lactose tolerant gene, it would be useless since animals haven't been domesticated yet.

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