Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
Human populations show remarkable variation in the ability to digest lactose, the sugar found in milk. While most mammals stop producing the enzyme lactase after infancy, some human populations retain high levels of lactase activity throughout adulthood. This condition, called lactase persistence, allows individuals to digest lactose without discomfort. In contrast, people with lactose intolerance produce little lactase after childhood, leading to cramping, bloating, and other symptoms when they consume dairy products. The genetic basis of this difference provides a clear example of how DNA sequences and chromosome regions influence inherited traits.
The gene responsible for lactase production, LCT, is located on chromosome 2. In early life, the LCT gene is active in almost everyone because digesting breast milk is essential for infant survival. In most individuals worldwide, the LCT gene is gradually switched off during childhood as part of normal developmental gene regulation. However, in several populations - especially those with long histories of dairy farming - mutations in a nearby regulatory region allow the LCT gene to remain active into adulthood.
Diagram 1.
Source: https://www.genovate.com/product/lactose-intolerance-dna-test/
These regulatory mutations do not alter the lactase protein itself. Instead, they change the activity of DNA sequences called enhancers, which affect how strongly the LCT gene is expressed. Individuals who inherit at least one copy of a lactase-persistence variant typically continue producing lactase throughout adulthood. Those without the variant experience reduced lactase expression and lactose intolerance. This is a powerful example of how DNA sequences and chromosomal organization work together to produce characteristic traits.
Global datasets show striking patterns: northern European populations have very high frequencies of lactase persistence, while many East Asian, Native American, and West African populations show low frequencies. These patterns reflect historical interactions between cultural practices – such as dairy farming – and natural selection acting on DNA variants.
Diagram 2.
Source: https://www.yogurtnutrition.com/lactase-activity/
On the molecular level, lactase persistence demonstrates how genes contain the instructions for proteins, while nearby DNA regions control when those instructions are used. Because these regulatory DNA sequences are inherited, the trait persists across generations.
Table 1.
Population | Lactase Persistence Frequency (%) |
|---|---|
Northern Europe | 90 |
East Asia | 10 |
West Africa | 25 |
Middle East | 60 |
North America | 40 |
South Asia | 30 |
Graph of Information - Figure 1.
Table 2.
Genotype | Average Lactase Activity (units/mL) |
|---|---|
AA | 18 |
AG | 12 |
GG | 4 |
Graph of Information - Figure 2.
Using Table 1 and Figure 1, describe one mathematical pattern in lactase persistence frequencies across global populations.
Using the reading and Diagram 1, explain how the presence or absence of the lactase enzyme affects digestive system function.
According to Table 2, which genotype shows the highest lactase activity?
Based on Table 2 and Figure 2, which genotype is most strongly associated with lactase non-persistence?
Using Table 2, Figure 2, and the description of regulatory DNA, explain how genotype relates to lactase enzyme activity levels.
Explain how DNA – including both the LCT gene and nearby regulatory sequences – accounts for differences in lactase persistence among human populations.
Respond using Claim, Evidence, and Reasoning.