To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video
The question panel opens below the video.
A. glucose only
The lactase enzyme breaks down lactose, a complex sugar (disaccharide), into two simple sugars (monosaccharides). Glucose is one of them. What is the other? Try again.
B. fructose only
The lactase enzyme breaks down lactose, a complex sugar (disaccharide), into two simple sugars (monosaccharides). Fructose is a simple sugar, but it is not produced by the digestion of lactose. Try again.
C. glucose and galactose
Correct! The complex sugar lactose (disaccharide) cannot pass through the lining of the small intestine. Lactase is an enzyme produced by cells lining the intestine. Lactase breaks lactose down into the two simpler sugars (monosaccharides) glucose and galactose, which can enter the bloodstream. Click to view an illustration of this process. Select another correct answer. You selected all the correct answers.
D. fructose and galactose
The lactase enzyme breaks down lactose, a complex sugar (disaccharide), into two simple sugars (monosaccharides). Galactose is one of them. What is the other? Try again.
If you need to review any part of the video before answering the question, you can scroll up and click on the timeline.
A. Someone who is able to digest lactose as an adult.
Correct! A lactase-persistent individual never stops making the enzyme lactase and can therefore easily digest lactose throughout their lives. Select another correct answer. You selected all the correct answers.
B. Someone who is unable to digest and tolerate lactose as an adult.
Review what lactase does. Also, the term persistent means "continuing to exist for a long period of time." How does the definition apply to the answer? Try again.
C. Someone who is unable to digest and tolerate lactose as a child.
Almost all mammals can digest and tolerate lactose when they are first born because their intestines produce the enzyme lactase. Review what lactase does. Also, the term persistent means "continuing to exist for a long period of time." How does the definition apply to the answer? Try again.
D. Someone who is able to digest and tolerate lactose as a child but who loses the ability as an adult.
A. Arthur, because his glucose level goes down.
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.
B. Rachel, because her glucose level returns to her baseline level.
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.
C. Peter and Sarah, because their glucose levels increase dramatically after drinking milk.
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.
D. Peter, Rachel, and Sarah, because their glucose levels went up after drinking milk.
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.
A. They are found in the part of DNA that encodes lactase ("the lactase gene").
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.
B. They are found in a noncoding regulatory region (a "switch") near the lactase gene.
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.
C. The mutations that cause lactase persistence in European and African populations are identical.
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.
D. The mutations that cause lactase persistence in European and African populations affect different genes.
The mutations that cause lactase persistence in European and African populations affect the same gene. Try again.
A. Ancient pots used to hold milk are about the same age as the lactase-persistence mutations.
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.
B. The lactase gene is present in both humans and domesticated animals.
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.
C. Present-day milk fats and animal body fats can be distinguished using carbon isotope analysis and gas chromatography.
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.
D. Scientists have discovered different mutations for lactase persistence in different cultures.
This is true, but it doesn’t give any information about cultural influences on the evolution of lactase persistence. Try again.
A. Milk could have been a critical food source during times of famine.
Correct! If other sources of food aren’t available, milk can provide necessary nutrition to individuals that can digest it. Select another correct answer. You selected all the correct answers.
B. Milk is generally safer to drink than water.
Correct! Unlike untreated water, fresh milk is relatively uncontaminated with pathogens and parasites. Select another correct answer. You selected all the correct answers.
C. Milk is rich in proteins and fats.
Correct! Milk contains a lot of high-quality proteins and fats that make it an important nutrient-dense food source for individuals that can digest it. Select another correct answer. You selected all the correct answers.
D. Milk could have been given to babies as a source of nutrition.
Milk is almost always digestible by babies. This does not help to explain why some people maintain their ability to digest milk into adulthood. Try again.
A. A population that raises wheat and sheep.
Correct! Sheep can provide milk, which has about the same amount of lactose as cow's milk. Therefore, a lactase-persistence mutation could potentially be advantageous in this population. Select another correct answer. You selected all the correct answers.
B. A population that raises potatoes and chickens.
Without a domesticated source of lactose, a lactase-persistence mutation would not provide a selective advantage. What are domesticated sources of lactose? Try again.
C. A population that raises rice and tilapia fish.
D. A population that raises corn and beans.
