This lab shows how genes (the instructions for your body) change in a group of people over five generations. We are looking at the gene for lactose tolerance, which is what lets you drink milk without getting a stomachache.

Everyone starts with one "milk-drinking" gene (L) and one "no-milk" gene (l).

Test 1: No Survival Rules

In this test, the environment doesn't care if you can drink milk or not.

• The Rule: Everyone survives and has kids, no matter what genes they have.

• What Happens: The parents' genes are mixed up randomly for the next generation.

• The Result: The percentage of L and l genes stays almost the same—about 50/50. Since no one is "leaving" the group, the genes don't really change.

Test 2: The Survival Test

In this test, being able to drink milk is a huge deal for survival!

• The Rule: Only people who can drink milk (LL or Ll) survive to have kids. People who get the l l genes do not pass them on.

• What Happens: Because the "no-milk" people are removed, fewer l l genes are left to be passed down.

• The Result: By the 5th generation, the L (milk-drinking) gene becomes much more common, often jumping to 80% or higher. The l l gene starts to disappear because it isn't helping anyone survive.