AP BIOLOGY

Detailed explanation-1: -Gradually, a mutation in the gene coding for the enzyme lactase made individuals “lactose tolerant”. This mutation spread across different human populations, giving them the advantage of being able to digest lactose. Thus, lactose tolerance is an example of a beneficial mutation.

Detailed explanation-2: -All humans can digest milk in infancy. But the ability to do so as an adult developed fairly recently, likely in the past 6000 years. A handful of mutations allows adults to produce the enzyme lactase, which can break down the milk sugar lactose.

Detailed explanation-3: -A single point mutation in the DNA near to the lactase gene changes the cytosine (C) nucleotide to a thymine (T). Individuals who have the thymine (T) nucleotide are lactose tolerant and can digest milk products in adulthood.

Detailed explanation-4: -Today, the ability to digest milk as an adult seems like a clear benefit, but that wasn’t always the case. Lactose tolerance is only advantageous in environments and cultures where humans have access to domesticated dairy animals.