AP Biology Exam Preparation

Lecturer Information

• Glenn Wolkenfeld, retired AP Biology teacher
• Topics covered: Meiosis, Mendelian genetics, non-Mendelian genetics, linkage, recombination
• Resources: Checklist available at AP bios.

Meiosis

Overview

• Meiosis is crucial for sexually reproducing eukaryotes (animals, plants, fungi, protists).
• Transmits genes from one generation to the next, creating variation.

Key Terms

• Haploid and Diploid Cells: Parents have two sets of chromosomes (diploid) except in gametes (haploid).
• Homologous Chromosomes: Matching chromosomes inherited from each parent; same genes, different alleles.

Process

• Reduction Division: DNA replication followed by meiosis 1 (homologous pairs separated) and meiosis 2 (sister chromatids separated).
• Variation Creation: Independent assortment and crossing over.

Comparisons

• Mitosis vs Meiosis
  • Mitosis: Growth and repair, one round of division, daughter cells are clones.
  • Meiosis: Reproduction, two rounds of division, introduces variation, haploid gametes.

Genetic Variation in Meiosis

• Independent Assortment: Chromosome pairs align independently during metaphase; creates diverse gametes.
• Crossing Over: Exchange of DNA segments during prophase 1; creates recombinant chromosomes.

Chromosomal Inheritance

Sex Determination

• Mammals: Determined by sperm (X or Y chromosome).
• Birds: Determined by egg (Z or W chromosome).
• Temperature-dependent: In reptiles, egg incubation temperature can determine sex.

Haplo-Diploid System

• Ants, Bees, Wasps: Females are diploid, males are haploid.

Non-Disjunction

• Failure of chromosomes to separate during meiosis; can lead to disorders like Down syndrome (trisomy 21).

Mendelian Genetics

Key Concepts

• Genes are units of heredity, passed from parents to offspring.
• Principle of Segregation: Each individual has two alleles per gene but passes only one to the offspring.
• Dominant and Recessive Alleles: Dominant alleles mask recessive ones in heterozygotes.

Genetic Crosses

• Monohybrid Cross: Cross between two heterozygotes, 3:1 phenotype ratio.
• Dihybrid Cross: Cross between two double heterozygotes, 9:3:3:1 phenotype ratio.

Non-Mendelian Genetics

Linkage

• Genes located on the same chromosome do not assort independently.
• Test Crosses: Used to determine recombination frequency and gene distance.

Recombinant Phenotypes

• Crossing over can create new allele combinations despite linkage.
• Recombination frequency reflects the distance between linked genes.

Other Genetic Concepts

Sex-linked Traits

• Located on the X chromosome, more common in males (e.g., hemophilia).

Non-Nuclear Inheritance

• Mitochondrial and chloroplast genes are inherited maternally.

Incomplete Dominance

• Heterozygous phenotype is intermediate (e.g., pink carnations).

Genotype-Environment Interaction

• Environment influences gene expression, affecting phenotype (e.g., hydrangeas' color, Himalayan rabbits' fur).

Resources

• Learnbiology.com offers interactive tutorials, quizzes, and a comprehensive AP Bio exam review system.