AP Biology Study Guide- Heredity, Genetics, and More

AP Biology Study Guide

Heredity & Genetics

Mendelian Genetics

• Gregor Mendel: Studied pea plants to understand heredity.

• Punnett Squares: Predicts offspring genotypes and phenotypes.

• Laws of Inheritance: Mendel’s claims about offspring inheritance parental traits

• Law of Dominance: One allele can mask another.

• Law of Segregation: Alleles separate during gamete formation.

• Law of Independent Assortment: Genes separate independently.

Non-Mendelian Genetics

• Incomplete Dominance: Blended traits (e.g., red + white flower → pink).

• Codominance: Both alleles are expressed (e.g., AB blood type).

• Polygenic Traits: Multiple genes affect a trait (e.g., skin color).

• Sex-Linked Traits: Genes located on X or Y chromosomes (e.g., color blindness).

Chi-Square Analysis

• Chi-Square Test: Determines if observed data fits expected results.

• Null Hypothesis (H₀): No significant difference between observed and expected values.

• p-value < 0.05: Reject H₀ (significant difference).

• p-value > 0.05: Fail to reject H₀ (differences likely due to chance).

Meiosis & Inheritance

• Meiosis: Produces gametes (sperm & egg) with half the chromosomes.

• Stages:

1. Interphase: DNA replicates.

2. Meiosis I: Homologous chromosomes separate.

3. Meiosis II: Sister chromatids separate.

• Genetic Variation:

• Crossing Over (Prophase I): Homologous chromosomes swap segments.

• Independent Assortment (Metaphase I): Chromosome pairs align randomly.

• Random Fertilization: Any sperm can fertilize any egg.

Meiosis Errors

• Nondisjunction: Failure to separate chromosomes.

• Trisomy 21 (Down Syndrome): Extra chromosome 21.

• Turner Syndrome (XO): Missing X chromosome in females.

• Klinefelter Syndrome (XXY): Extra X chromosome in males.

Population Genetics & Evolution

Hardy-Weinberg Equilibrium

• Equation: p² + 2pq + q² = 1

• Conditions for Equilibrium(no evolution occurs):

1. No mutations.

2. No natural selection.

3. No gene flow.

4. Large population.

5. Random mating.

Mechanisms of Evolution

• Genetic Drift: Random changes in allele frequencies (small populations affected more).

• Bottleneck Effect: Drastic reduction in population size.

• Founder Effect: Small group colonizes new area.

• Gene Flow: Movement of alleles between populations.

• Natural Selection: Traits that improve survival & reproduction increase in frequency.

Speciation & Evolution

Types of Speciation

• Allopatric Speciation: Geographic isolation leads to new species.

• Sympatric Speciation: New species arise in the same location (e.g., genetic mutations).

Barriers to Reproduction

• Prezygotic Barriers: Prevent fertilization.

• Temporal (different mating times), behavioral, mechanical, gametic isolation.

• Postzygotic Barriers: Prevent viable offspring.

• Hybrid inviability, hybrid sterility (e.g., mules).

Rates of Evolution

• Gradualism: Slow, continuous change.

• Punctuated Equilibrium: Rapid bursts of change followed by stability.

Key Experiments & Scientists

• Charles Darwin: Theory of natural selection.

• Gregor Mendel: Laws of inheritance.

• Thomas Hunt Morgan: Linked genes on chromosomes.

• Hardy-Weinberg: Population genetics principles.