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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]
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] The sequence is highly conserved in mammals, suggesting that critical cis-transcriptional regulators ...
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]
Infant mammals nurse on their mothers to drink milk, which is rich in lactose. The intestinal villi secrete the enzyme lactase (β-D-galactosidase) to digest it. This enzyme cleaves the lactose molecule into its two subunits, the simple sugars glucose and galactose, which can be absorbed. Since lactose occurs mostly in milk, in most mammals ...
In most mammals, production of lactase diminishes after infants are weaned from maternal milk. However, 5% to 90% of the human population possess an advantageous autosomal mutation in which lactase production persists after infancy. The geographic distribution of lactase persistence is concordant with areas of high milk intake.
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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. [15]