Which mutation is commonly cited as enabling adults to digest lactose?

• A. CCR5-delta32 providing HIV resistance
• B. Sickle cell trait
• C. Albinism
• D. Lactase persistence into adulthood

Answer: (D)

Lactase persistence is the genetic trait that lets adults digest lactose. Normally, the enzyme lactase drops off after weaning, so most adults become lactose intolerant. But a regulatory variant in the region near the lactase gene keeps the gene active into adulthood, so enzyme production continues and lactose can be broken down in the intestine.

This trait is a classic example of how a genetic change can alter metabolism in adulthood and has been shaped by the history of dairy farming in human populations. The other options describe mutations linked to different traits (HIV resistance, malaria resistance, or pigmentation) and do not affect the ability to digest lactose.