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Volume I · MMXXVI AP Biology
Library› AP Biology› Unit 5: Heredity
⁂   AP Biology · Unit 5

5. Heredity

8–11% of the AP exam. 8 key topics. 4 common errors analyzed.

8–11% exam weight 10 instructional periods

Unit 5: Heredity

Unit 5 covers heredity — a core component of the AP Biology curriculum. Master these concepts to build the mechanistic vocabulary the FRQ rubrics demand.

Key topics in this unit

  1. Meiosis I and II: stages, chromosome behavior, comparison with mitosis
  2. Sources of genetic variation: crossing over (recombination), independent assortment, random fertilization
  3. Mendelian genetics: law of segregation, law of independent assortment
  4. Monohybrid and dihybrid crosses using Punnett squares
  5. Dominant, recessive, and codominant alleles; incomplete dominance
  6. Sex-linked (X-linked) inheritance patterns
  7. Polygenic traits and continuous variation
  8. Chi-square (χ²) statistical test for goodness-of-fit in genetics problems

Common errors — what the rubric penalizes

These are the most frequently penalized mistakes on AP exam FRQs and MCQs. Review each before your next practice session.

Common error

Forgetting to square p and q when calculating homozygous genotype frequencies in Hardy-Weinberg problems (writing p instead of p²)

Common error

Confusing crossing over (occurs in prophase I of meiosis between homologs) with independent assortment (random orientation of bivalents at metaphase I)

Common error

Applying the product rule to non-independent events or the sum rule to non-mutually exclusive events in probability problems

Common error

Misidentifying the expected ratio for a dihybrid cross as 9:3:3:1 without verifying that the two genes assort independently

Study checklist

  • Can you list all key topics from memory without this page?
  • Have you worked through at least one FRQ-style question per topic?
  • Can you explain each common error above — and why the correct answer differs?
  • Have you reviewed the relevant College Board CED section and formula sheet entries?
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