The type of mutation that occurred 7500 years ago in central Europe - VCE - SSCE Biology - Question 7 - 2020 - Paper 1

The frequency of the allele for lactase persistence increased relatively quickly due to several factors. Firstly, individuals in populations where milk constituted a significant part of their diet experienced a selective advantage, as they could digest lactose efficiently and utilize it as an energy source. This higher survival and reproductive success led to a greater number of offspring carrying the allele.

Secondly, when individuals with the mutation were chosen for reproduction, they produced more offspring compared to those without the mutation. This phenomenon contributed to the rapid increase in allele frequency within smaller, isolated populations. Lastly, strong selection pressure favored those with the mutation, further accelerating the rate at which this beneficial trait spread throughout the population.

There are a couple of reasons for the absence of the mutation in some present-day populations. One reason is that some populations do not rely on dairy products as a primary food source, which diminishes the selective advantage of being able to digest lactose.

Another reason is that in these populations, individuals may not have had access to the milk and dairy products historically, contributing to the lack of evolutionary pressure to maintain the lactase persistence allele. Thus, over generations, the mutation may have been lost due to genetic drift and the absence of positive selection.