Unit 5 · Heredity
The Complete AP Biology Guide · AP BiologyUnit 5 · Heredity
- The Complete AP Biology Guide
- AP Biology
- 8 sections
Unit 5: Heredity accounts for 8% to 11% of the AP Biology exam score in Section I (multiple choice), and its mechanisms also appear in Section II free-response questions. Heredity problems become unstable when homologs, sister chromatids, alleles, gametes, genotypes, and phenotypes are treated as interchangeable.
- How AP Biology assesses this 8–11% of the Section I score · mechanisms recur in Section II FRQs · 60 MCQs in 90 min
- Key skills meiosis and genetic diversity, inheritance patterns, genotype environment and phenotype
- How to study for Unit 5 You will use chromosome bookkeeping and conditional probability to connect meiosis to inheritance while keeping linkage, nondisjunction, environment, and statistical evidence in their correct layers.
- The organizing decision Which chromosome copies and alleles can enter each gamete under the stated meiotic event, and what observations would distinguish the resulting inheritance model?
Unit 5: Heredity accounts for 8% to 11% of the AP Biology exam score in Section I (multiple choice), and its mechanisms also appear in Section II free-response questions.
Weighting is the College Board CED range for the current exam. Higher-weight units repay proportionally more review time; use this share to size your effort before drilling the mechanisms below. See the AP Biology exam guide & review for all eight units.
Heredity problems become unstable when homologs, sister chromatids, alleles, gametes, genotypes, and phenotypes are treated as interchangeable. A chromosome diagram describes physical behavior, a probability model describes possible outcomes, and offspring data test whether that model fits the observed inheritance pattern.
You will use chromosome bookkeeping and conditional probability to connect meiosis to inheritance while keeping linkage, nondisjunction, environment, and statistical evidence in their correct layers.
The decision that organizes this unit
Which chromosome copies and alleles can enter each gamete under the stated meiotic event, and what observations would distinguish the resulting inheritance model?
Mechanism route and repair branches
- Main route: Identify homologous chromosomes, sister chromatids, loci, and parental allele arrangements before following a division.
- Main route: Track replication separately from homolog separation and sister-chromatid separation so chromosome and DNA-copy counts remain consistent.
- Diagnostic cue: DNA replication is said to double chromosome number. Wrong branch: Chromatid copies and chromosomes are counted as the same object. Repair: Count chromosomes by centromeres and DNA copies by chromatids, then state which structures separate at each meiotic division.
- Main route: List possible gametes under independent assortment, linkage, crossing over, or nondisjunction before combining parental probabilities.
- Diagnostic cue: Linked loci are multiplied as independent probabilities. Wrong branch: Independent assortment is applied without checking chromosome location. Repair: Use parental arrangement and recombination evidence; only use the product rule after the relevant events are justified as independent.
- Main route: Translate gamete combinations into offspring genotypes, then use the stated dominance, interaction, or environmental relation to predict phenotype.
- Diagnostic cue: A genotype is claimed to determine one phenotype in every environment. Wrong branch: Gene expression and environmental effects disappear from the model. Repair: State the genotype-dependent capacity and then include the environmental condition or interaction that changes the measured phenotype.
- Main route: Compare observed and expected counts with an appropriate model, preserving degrees of freedom and the limits of the statistical conclusion.
