Question

45. In which human tissue might you expect to find high expression of LCT and why is lactase persistence an advantage to humans who have close relationships with dairy cattle?

Answer 1

In the wall lining of small intestine lactase cells are found . These cells are called intestinal epithelial cells. The  finger-like projections called microvilli which are present at the wall of intestine help in  absorption of nutrients from food as it passes through the intestine and in turn   it is absorbed into the bloodstream. These brush border cells help in break down of lactose into absorbable forms hence improve lactose function . All mammals at the begining of life feed on milk and hence have the ability to digest lactose. This characteristic is advantageous during the infant stage . But with ageing in mamnals weaning occurs, and we used to eat other foods also and are not solely dependent on milk . So with time this ability to digest lactise is no longer a distinct fitness advantage .   The mammalian lactase gene (LCT) expression slow downs or decreases after the weaning stage which causes less production of lactase enzymes. This also results in lactase non-persistence (LNP). So we can infer from this  lactase persistent phenotype involves high mRNA expression that is high lactase activity means the high ability to digest lactose.  The lactase nonpersistent expression results in low mRNA expression and low lactase activity.