DNA mystery: milk tolerance
Infants can break down lactose — but in many adults the enzyme partly shuts off. A variant near the LCT gene often decides whether milk tolerance stays.
What share of the world's adults can digest milk?
A minority — lactose tolerance is historically new, most common in Northern Europe.
The marker rs4988235 near LCT is the most cited variant for adult lactase persistence. In Northern Europe tolerance is common; globally the majority of adults are lactose intolerant to some degree.
Tolerance is a scale, not on/off: amount, food habits and gut flora also play a role.
Marker: the MCM6/LCT region — rs4988235. Look it up, or check your own variant against your raw data file — locally in the browser, no upload.