AP Biology / Unit 7
AP Biology Unit 7: Natural Selection
Unit 7 is the highest-value AP Biology unit for many students because it combines evolution, statistics, population reasoning, and evidence-based explanation.
What this unit covers
- Natural selection
- Hardy-Weinberg equilibrium
- Population genetics
- Speciation
- Phylogenetics
Why students lose points here
- They confuse random change with selection.
- They can do the math but cannot explain what it means.
- They forget to connect data to the evolutionary claim.
- They miss the difference between a change in allele frequency and a change in a single organism.
What to focus on
- Natural selection versus genetic drift.
- Allele frequencies and Hardy-Weinberg.
- Evidence for evolution.
- How environments shape populations over time.
FRQ patterns
Unit 7 FRQs often ask students to:
- interpret a population change;
- justify a claim with evidence;
- explain a bottleneck or drift event;
- predict how allele frequencies shift.
Study tip
When you answer Unit 7, always separate random events from selection. That distinction is often the point.
FAQ
How much of the AP Biology exam is Unit 7?
Unit 7 (Natural Selection) accounts for 13–20% of the multiple-choice section — the single highest-weight unit on the AP Biology exam.
What's the difference between natural selection and genetic drift?
Natural selection is non-random: alleles change frequency because they affect survival or reproduction. Genetic drift is random: allele frequencies change by chance, especially in small populations. Conflating the two is one of the most common point-losers on Unit 7 FRQs.
Do I need to memorize the Hardy-Weinberg equations?
No. The Hardy-Weinberg equations are on the formula sheet provided on exam day. You do need to know how to apply them — that's where Unit 7 points are won or lost.
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