Interactive Video: Got Lactase? The Co-Evolution of Genes and Culture: HHMI BioInteractive

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A line graph showing four individuals' blood glucose levels over time. The x-axis is in minutes, ranging from zero to sixty in intervals of 15 minutes. The y-axis is blood glucose levels measured in milligrams per deciliters, ranging from 80 to 160. Peter, Rachel and Arthur start with a blood glucose level at approximately 95. Sarah begins with a blood glucose level or approximately 108. Sarah and Peter’s blood glucose levels rise and peak around 45 minutes, with Peter’s measuring approximately 155 milligrams per deciliter and Sarah’s measures 140. Rachel’s blood glucose level rises slightly, peaking at 30 minutes, measuring approximately 105 milligrams per deciliter. Arthur’s blood glucose decreases, with a low of approximately 85 milligrams per deciliter at 45 minutes.

Four individuals measured their baseline blood glucose, then quickly drank a liter of milk. They then measured their blood glucose levels at regular 15-minute intervals for 60 minutes. The results are shown in the graph. Which individual or individuals are lactase persistent, and how do you know?

Lactase breaks down lactose into glucose and galactose. If a lactase-persistent person drinks milk, would you expect his or her glucose levels to increase or decrease? Try again.

Lactase breaks down lactose into glucose and galactose, so if a person is lactase persistent, their glucose levels should increase quite dramatically after drinking a liter of milk. Rachel's levels do increase but only slightly, and they quickly return to her baseline level. Try again.

Correct! Peter and Sarah's blood glucose levels both rose by more than 30 mg/dL, showing that their bodies were producing lactase, which broke down the lactose in the milk to glucose and galactose. The molecules were then absorbed in the bloodstream and the increase in glucose was measured. Select another correct answer. You selected all the correct answers.

Lactase breaks down lactose into glucose and galactose, so if a person is lactase persistent, you'd predict that his or her glucose levels should dramatically increase after drinking a liter of milk. The data from two—not three—of the individuals in this test match that prediction. Try again.

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What did researchers discover about genetic mutations that cause lactase persistence?

A mutation to the lactase gene itself could alter the structure and function of lactase. Such mutations could be highly disadvantageous, if not lethal, if they altered an infant’s ability to digest their mother’s milk. Try again.

Correct! All known mutations giving rise to lactase persistence are in a genetic "switch" that regulates the activity of the lactase gene. Mutations in regulatory regions can affect the expression of a protein (how much, where, and when it is produced) without affecting its structure or function. Select another correct answer. You selected all the correct answers.

Researchers expected to find the same mutations among the different populations, but the mutation that causes lactase persistence in Europe was almost entirely absent in Africa. Try again.

The mutations that cause lactase persistence in European and African populations affect the same gene. Try again.

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Which discovery best supports the hypothesis that evolution of the lactase-persistence trait was driven by dairying, the use of milk as a source of adult nutrition in pastoralist cultures?

Correct! Agreement between archaeological and genetic data provides strong evidence for early milk use and the co-evolution of genes and culture in pastoral populations. Select another correct answer. You selected all the correct answers.

All mammals have the lactase gene so infants can digest their mother's milk, but that doesn't provide any information about how lactase persistence evolved in certain human populations. Try again.

This is true, but the ability to distinguish the different kinds of fats doesn't itself give any information about the evolution of lactase persistence. To get that information, you have to get data from ancient—not present-day—sources. Try again.

This is true, but it doesn’t give any information about cultural influences on the evolution of lactase persistence. Try again.

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