Ap Bio Unit 5 Review

AP Bio Unit 5 Review: Cracking the Code of Heredity and Evolution

This comprehensive review covers AP Biology Unit 5, focusing on heredity and evolution. Understanding these concepts is crucial for success on the AP exam. We'll delve into the intricacies of genetics, from Mendelian inheritance to population genetics, and how these principles drive evolutionary change. This guide will equip you with the knowledge and strategies to confidently tackle any question related to this vital unit.

I. Mendelian Genetics: The Foundation of Heredity

This section revisits the fundamental principles of inheritance discovered by Gregor Mendel. Understanding Mendel's Laws is the cornerstone of comprehending more complex genetic phenomena.

• Mendel's Laws:

  • Law of Segregation: Alleles for a gene separate during gamete formation, resulting in each gamete carrying only one allele for each gene.
  • Law of Independent Assortment: Alleles for different genes segregate independently during gamete formation. This holds true for genes located on different chromosomes or those far apart on the same chromosome.

• Key Terms:

  • Gene: A unit of heredity that occupies a specific locus on a chromosome.
  • Allele: Alternative forms of a gene.
  • Genotype: The genetic makeup of an organism.
  • Phenotype: The observable characteristics of an organism.
  • Homozygous: Having two identical alleles for a gene (e.g., AA or aa).
  • Heterozygous: Having two different alleles for a gene (e.g., Aa).
  • Dominant Allele: An allele that masks the expression of a recessive allele when present.
  • Recessive Allele: An allele whose expression is masked by a dominant allele.
  • Punnett Square: A diagram used to predict the genotypes and phenotypes of offspring from a genetic cross.
  • Test Cross: A cross between an individual with an unknown genotype and a homozygous recessive individual to determine the unknown genotype.

• Beyond Simple Dominance:

  • Incomplete Dominance: Neither allele is completely dominant; the heterozygote shows an intermediate phenotype (e.g., red flower x white flower = pink flower).
  • Codominance: Both alleles are fully expressed in the heterozygote (e.g., AB blood type).
  • Multiple Alleles: More than two alleles exist for a gene (e.g., ABO blood group system).
  • Pleiotropy: A single gene affects multiple phenotypic traits.
  • Epistasis: The expression of one gene is affected by another gene.
  • Polygenic Inheritance: Multiple genes contribute to a single phenotypic trait (e.g., human height, skin color).

II. Extending Mendelian Genetics: Beyond the Basics

Mendelian genetics provides a solid foundation, but many inherited traits exhibit more complex patterns.

• Sex-linked Inheritance: Genes located on the sex chromosomes (X and Y) exhibit unique inheritance patterns. X-linked recessive traits are more common in males because they only have one X chromosome.
• Linked Genes: Genes located close together on the same chromosome tend to be inherited together. Recombination frequency can be used to map the distance between linked genes.
• Chromosome Aberrations: Changes in chromosome structure (deletions, duplications, inversions, translocations) or number (aneuploidy, polyploidy) can lead to various genetic disorders.
• Genetic Mapping: Determining the relative positions of genes on a chromosome using recombination frequencies.

III. Molecular Basis of Inheritance: DNA and its Role

This section explores the molecular mechanisms underlying inheritance.

• DNA Structure and Replication: The double helix structure of DNA, its replication via semi-conservative replication, and the roles of enzymes like DNA polymerase and helicase.
• Transcription and Translation: The processes of converting DNA into RNA (transcription) and RNA into protein (translation). The roles of mRNA, tRNA, rRNA, ribosomes, and the genetic code.
• Gene Regulation: Mechanisms that control gene expression, including operons (e.g., lac operon), transcription factors, and epigenetic modifications.
• Mutations: Changes in the DNA sequence that can lead to altered protein function and phenotypic changes. Different types of mutations (point mutations, frameshift mutations, chromosomal mutations) and their potential effects.
• Recombinant DNA Technology: Techniques used to manipulate DNA, such as PCR, restriction enzymes, gel electrophoresis, and cloning. Applications in biotechnology, medicine, and agriculture.

IV. Evolutionary Mechanisms: The Driving Forces of Change

This section integrates genetics with evolutionary principles.

• Population Genetics: The study of genetic variation within populations. Key concepts include allele frequencies, genotype frequencies, the Hardy-Weinberg equilibrium, and factors that disrupt this equilibrium.
• Hardy-Weinberg Equilibrium: A model that describes a population not undergoing evolutionary change. The five conditions for Hardy-Weinberg equilibrium are: no mutation, random mating, no gene flow, large population size, and no natural selection. The equation p² + 2pq + q² = 1 is used to calculate allele and genotype frequencies.
• Mechanisms of Evolution: Factors that alter allele frequencies in populations:
  • Mutation: The ultimate source of genetic variation.
  • Gene Flow: The movement of alleles between populations.
  • Genetic Drift: Random fluctuations in allele frequencies, particularly significant in small populations (bottleneck effect and founder effect).
  • Non-random Mating: Mating preferences that can alter genotype frequencies (e.g., assortative mating, disassortative mating).
  • Natural Selection: The differential survival and reproduction of individuals based on their traits. This leads to adaptive evolution. Different types of selection (directional, stabilizing, disruptive).
• Speciation: The formation of new and distinct species. Different modes of speciation (allopatric, sympatric).
• Phylogenetic Trees: Diagrams that represent the evolutionary relationships among different species.

V. Evidence for Evolution: The Proof is in the Pudding

This section highlights the various lines of evidence supporting the theory of evolution.

• Fossil Record: Provides evidence of extinct species and the transition of species over time.
• Biogeography: The distribution of species across geographical areas provides clues about their evolutionary history.
• Comparative Anatomy: Similarities in the anatomy of different species (homologous structures, analogous structures, vestigial structures) suggest common ancestry.
• Comparative Embryology: Similarities in the embryonic development of different species support common ancestry.
• Molecular Biology: Similarities in DNA and protein sequences provide strong evidence for evolutionary relationships.

VI. Putting it All Together: Applying Your Knowledge

This section provides strategies for applying your knowledge to AP exam questions.

• Practice Problems: Work through a variety of practice problems to reinforce your understanding of the concepts.
• Multiple Choice Questions: Practice answering multiple-choice questions that test your knowledge of the key terms, concepts, and processes.
• Free Response Questions: Practice writing free-response answers that require you to apply your knowledge to specific scenarios.
• Review Key Terms and Concepts: Make sure you have a solid understanding of all the key terms and concepts discussed in this review.
• Understand the Relationships: Focus on understanding the relationships between different concepts. For example, how Mendelian genetics relates to population genetics and how both contribute to our understanding of evolution.

VII. Frequently Asked Questions (FAQ)

• What is the difference between genotype and phenotype? Genotype refers to the genetic makeup of an organism, while phenotype refers to its observable characteristics.
• What are the conditions for Hardy-Weinberg equilibrium? No mutation, random mating, no gene flow, large population size, and no natural selection.
• What are the different types of natural selection? Directional, stabilizing, and disruptive.
• What is the difference between homologous and analogous structures? Homologous structures share a common ancestry, while analogous structures have similar functions but different origins.
• What is the role of genetic drift in evolution? Genetic drift causes random fluctuations in allele frequencies, particularly in small populations.

VIII. Conclusion: Mastering AP Bio Unit 5

This comprehensive review provides a solid foundation for mastering AP Biology Unit 5. Remember, consistent effort and practice are key to success. By thoroughly understanding Mendelian genetics, extending your knowledge to molecular mechanisms, grasping evolutionary principles, and practicing with exam-style questions, you'll be well-prepared to excel on the AP Biology exam. Good luck!