Lactose Intolerance: An Ancestral Trait
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- The enzyme lactase digests lactose, the sugar in milk.
- The lactase gene is active in infants, and they are lactose tolerant.
- After weaning, humans stop producing lactase and become lactose intolerant.
- Some people carry a mutation that keeps the lactase gene switched on past infancy, resulting in what is called lactase persistence or lactose tolerance.
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