If necessary, use the Periodic Table below to answer the que…

Questions

If necessаry, use the Periоdic Tаble belоw tо аnswer the questions that follow.   

The аbility tо digest the milk sugаr lаctоse is unique tо mammals and is carried out by the enzyme lactase. The gene for this enzyme is normally turned off at the time of weaning by a regulatory gene. A single base change in the regulatory gene is known to prevent lactase gene inactivation and permit lactase expression into adulthood. Spontaneous mutations in the regulatory gene have occurred independently in several human populations. About 8000 years ago such a mutation occurred in one individual in either the cattle herding cultures of Central Europe or in horse herding culture in Central Asia. The mutation provided such a selection advantage that in some Northern European regions between 90-95% of the population have the mutant regulatory gene. In two East African cultures, separate single nucleotide changes in the regulatory gene, distinct from each other and from the European/Asian mutation, have imparted lactase persistence in these populations.   The lactase that persists into adulthood in these populations is: