Lactose tolerant individuals

Question

Why can individuals from only some human populations tolerate milk as adults? In your own words, explain in detail the genetic changes that allow for milk tolerance in adult humans.)

Answer 1

In the 1960s, researchers supported the fact that the groups of human population involved in cattle domestication are lactose tolerance. About 3000-7,000 years ago, when goats and cattle first became domesticated, a rich source of protein rich became available in the form of milk. Research findings highlights the fact that the adults belongs to the sector of population involved in domestication of cattle were only able to digest milk.

Later in 1970's, research findings indicated that a genetic mutation is responsible for lactase persistence.

Thus, it depicts that lactase persistence population was coincidental with the rise of cattle domestication. This mutation has retained almost half of the world’s population to metabolize lactose.

In 2002, a group of Finnish researchers have supported the fact that a genetic mutation is responsible for lactase persistence in North Europeans. The genetic ground for this common metabolic abnormality is due to the  mutation in a regulatory region of the Lactase gene (LCT T-13910C). The mutation at T-13910C 5' end before the Lactase gene (LCT T-13910C), the gene for coding Lactase enzyme, seem to be the reason for Lactose Intolerance.

Another reason reported by them was, the rare connatal form of lactose intolerance may occur due to two reasons:

i) By disabling mutations in the Lactase gene
ii) Complete deletion.

A small alteration in an enhancer region upstream of the lactase gene turn off the gene expression after early childhood. In some individuals,  Lactase gene (LCT T-13910C) is  switched off as children gradually deprive of mother's milk and leads to lactose intolerance in adults.