Laboratory Experiment 8: Population Genetics and Evolution for AP Biology
This experiment reviews material from evolution. After completing this experiment, you want to be sure you know how to use the Hardy–Weinberg equation and how microevolution throws the whole concept of Hardy–Weinberg equilibrium out the window. I will not go into the gruesome detail again here. This lab also discusses the effects that natural selection can have on a population.
For a quick review on evolution, refer to the following concepts:
- Evolution for AP Biology
- Types of Selection for AP Biology
- Hardy–Weinberg Equilibrium and Evolution for AP Biology
The equations to know for this experiment are p + q = 1 and p2 + 2pq + q2 = 1. Back in Chapter 12, I listed five conditions required for the existence of Hardy– Weinberg equilibrium:
- Large population size (no genetic drift).
- Random mating.
- No mutation.
- No gene flow.
- No natural selection.
If any one of these five conditions does not hold true, then the population will experience microevolution, and the frequencies of the alleles will be subject to change.
The first part of this experiment examines how to experimentally measure the frequencies of certain alleles. The second part studies a population in Hardy–Weinberg equilibrium, and the final part examines heterozygote advantage—situation (e.g., sickle cell anemia in malarial regions) in which being heterozygous for a condition provides some benefit.
There is not really too much to this experiment. The class gets to be the heterozygous breeding population, and each student has the initial genotype of Aa. Each student is given four cards: two A cards and two a cards. These represent the four outcomes from meiosis. The experiment attempts to imitate a Hardy–Weinberg scenario by having students randomly find another person to exchange cards with to produce two offspring. After producing these offspring, both parents now pretend that they are the newly produced offspring, to mimic the creation of another generation. This process is to be repeated many times until enough data are collected. The point is to see if the allele frequency changes in the classroom as a whole by the end of the last generation as compared to the initial frequency of 50 percent A and 50 percent a. The results should be the same, but the size of the classroom might be in violation of the "large population" requirement for Hardy–Weinberg equilibrium, leading to a shift in the frequencies.
You can design an experiment to measure the effect of selection, heterozygote advantage, and genetic drift using a similar experiment structure:
Selection. Imagine that an individual homozygous recessive for the condition that the cards represent does not survive to reproduce. Each time two students exchange cards and produce an aa child, they simply exchange cards again until a different pairing is obtained. This is because the aa would not survive to reproduce anyway. This will cause a shift in allele frequencies to include more A children and fewer a children.
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