Mastering Biology HHMI: Got Lactase?

How does the term "lactase persistent" relate to the term "lactose tolerant"?

A lactase-persistent person is lactose tolerant. Because: a "lactase-persistent" adult continues to make the enzyme lactase and is able to digest (and tolerate) lactose.

The enzyme lactase breaks the sugar lactose into which compound(s)?

Galactose Glucose Because: the lactase enzyme breaks the lactose disaccharide into two monosaccharides, glucose and galactose.

Which discovery supports the hypothesis that evolution of the lactase-persistence trait was driven by the use of milk in pastoralist cultures?

Ancient pots used to hold milk are about the same age as the lactase-persistence mutation Because: evidence of early milk use in lactase-persistent cultures provides evidence for the co-evolution of genes and culture.

What did researchers discover about the genetic mutation causing lactase persistence?

It is found in a regulatory region (a "switch") upstream of the lactase gene Because: all known mutations giving rise to lactose persistence are in a genetic "switch" that regulates expression of the lactase gene. Mutations in regulatory regions can change the amount of protein that is produced without affecting its structure or function.

Suppose that a mutation for lactase-persistence occurred in each of the populations described below. In which populations would the mutation be more likely to increase in frequency over time because of natural selection?

a population that raises wheat and sheep Because: 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.

How could milk-drinking have provided strong favorable selection for lactase persistence?

Milk may have been a critical food source during times of famine. Milk is protein and fat-rich and therefore could have been an important, high-quality food source. Milk was safer to drink than water and reduced exposure to pathogens Because: all of these could have provided strong favorable selection for lactase persistence.

Four individuals measured their baseline blood glucose, then drank a litre of milk. They then measured their blood glucose levels at regular 15 minute intervals for 60 minutes. The results are shown in the graph below. Which individuals are lactase-persistent?

Sarah Peter Because: Peter and Sarah's blood glucose levels both rose by more than 30 mg/dL, showing that their bodies digested lactose into glucose and galactose.