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Lactase persistence or lactose tolerance is the continued activity of the lactase enzyme in adulthood, allowing the digestion of lactose in milk.In most mammals, the activity of the enzyme is dramatically reduced after weaning. [1]
English: Interpolated map of the percentage of adults with a known lactase persistence genotype (-14010 G>C, -13915 T>G, -13907 C>G or -13910 C>T) in the indigenous population of the Old World. Circles mark the sample locations.
Lactase persistence in humans evolved relatively recently (in the last 10,000 years) among some populations. Around 8,000 years ago in modern-day Turkey, humans became reliant on newly-domesticated animals that could be milked; such as cows, sheep, and goats. This resulted in higher frequency of lactase persistence. [79]
The majority of humans actually follow this protocol as well, and down-regulate lactase production around 3-5 years of age. Interestingly, though, the majority of caucasians, mainly those from northern european background, continue to have elevated lactase activity all the way into adulthood, and so they exhibit “lactase persistence”.
Lactase persistence is a rare ability among mammals. [73] Because it involves a single gene, it is a simple example of convergent evolution in humans. Other examples of convergent evolution, such as the light skin of Europeans and East Asians or the various means of resistance to malaria, are much more complicated.
Both mutations, C→T at position -13910 and G→ A at position -22018, have been independently linked to lactase persistence. [27] The lactase promoter is 150 base pairs long and is located upstream of the site of transcription initiation. [27]
Many adults are lactose intolerant because their bodies cease production of the enzyme lactase post childhood. However, mutations in the promoter region of the lactase gene (LCT) result in the continued production of lactase throughout adulthood in certain African populations, a condition known as lactase persistence. A study conducted by Sarah ...
Lactase persistence [ edit ] In one study, five ancient DNA samples from Yamnaya sites had a frequency of over 25% of an allele that is associated with lactase persistence , conferring lactose tolerance into adulthood . [ 45 ]