Question

What happens to the expression of the lactase gene when a baby is weaned from his or her mother's milk?

Answer 1

After mammalian infants are weaned from their mother's milk, the gene that produces lactase is turned off and the lactase protein is no longer present on the surface of the microvilli. Shutting down lactase production when it's no longer needed makes evolutionary sense.

In lactose tolerant individuals, that gene keeps working into adulthood, producing the protein that digests lactose and makes eating ice cream a pleasant experience. But in people who are lactose intolerant, that lactase gene is switched off after weaning.

( Weaning is the process of stopping feeding your baby with breast milk .

Lactase is an enzyme produced by many organisms , Lactase is essential to the complete digestion of whole milk; it breaks down lactose, a sugar which gives milk its sweetness. )