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 this unit is crucial for success on the AP exam because it connects fundamental concepts of genetics with the broader processes of evolution. We'll delve into Mendelian genetics, non-Mendelian inheritance, molecular genetics, and the mechanisms driving evolutionary change. This detailed review will equip you with the knowledge and tools needed to confidently tackle any question related to this vital unit.

I. Mendelian Genetics: The Foundation of Heredity

This section revisits the foundational principles established by Gregor Mendel. His experiments with pea plants revealed the basic patterns of inheritance.

Key Concepts:

• Genes, alleles, and loci: Understand the difference between a gene (a unit of heredity), an allele (different versions of a gene), and a locus (the specific location of a gene on a chromosome).
• Genotype and phenotype: Distinguish between genotype (the genetic makeup of an organism) and phenotype (the observable characteristics).
• Homozygous and heterozygous: Recognize the difference between homozygous (carrying two identical alleles for a trait) and heterozygous (carrying two different alleles).
• Dominant and recessive alleles: Understand the concept of dominant alleles (expressed even when paired with a recessive allele) and recessive alleles (only expressed when paired with another recessive allele).
• Punnett squares and probability: Master the use of Punnett squares to predict the probability of offspring inheriting specific genotypes and phenotypes. Remember to consider both monohybrid (single gene) and dihybrid (two gene) crosses.
• Test crosses: Understand how test crosses (crossing an unknown genotype with a homozygous recessive individual) can be used to determine the genotype of an individual exhibiting a dominant phenotype.

Example Problem: In pea plants, tallness (T) is dominant to shortness (t). If a homozygous tall plant (TT) is crossed with a homozygous short plant (tt), what are the genotypes and phenotypes of the F1 generation? What about the F2 generation if two F1 plants are crossed?

Solution:

• F1 generation: All offspring will be Tt (heterozygous) and tall (phenotype).
• F2 generation: Using a Punnett square, you'll find a 3:1 phenotypic ratio (3 tall: 1 short) and a 1:2:1 genotypic ratio (1 TT: 2 Tt: 1 tt).

II. Non-Mendelian Inheritance: Beyond Simple Dominance

Mendel's laws provide a solid foundation, but many inheritance patterns deviate from these simple rules.

Key Concepts:

• Incomplete dominance: Neither allele is completely dominant; the heterozygote displays an intermediate phenotype (e.g., pink flowers from red and white parents).
• 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: One gene affects multiple phenotypic traits (e.g., sickle cell anemia).
• Epistasis: The expression of one gene is influenced by another gene (e.g., coat color in Labrador retrievers).
• Polygenic inheritance: Multiple genes contribute to a single phenotypic trait (e.g., human height, skin color).
• Sex-linked traits: Genes located on sex chromosomes (X or Y) show different inheritance patterns in males and females (e.g., color blindness, hemophilia).

Example Problem: Explain why individuals with blood type AB have both A and B antigens on their red blood cells.

Solution: This is an example of codominance. Both the A and B alleles are fully expressed in heterozygotes (IAIB), resulting in the presence of both A and B antigens.

III. Molecular Genetics: The Mechanism of Inheritance

This section dives into the molecular basis of heredity, exploring the structure and function of DNA and its role in protein synthesis.

Key Concepts:

• DNA structure and replication: Understand the double helix structure of DNA, base pairing rules (A-T, G-C), and the semiconservative model of DNA replication.
• Transcription and translation: Master the processes of transcription (DNA to RNA) and translation (RNA to protein). Understand the roles of mRNA, tRNA, rRNA, codons, and anticodons.
• Gene expression and regulation: Explore how genes are turned on and off, including the roles of promoters, enhancers, silencers, and transcription factors.
• Mutations: Understand different types of mutations (point mutations, frameshift mutations, chromosomal mutations) and their potential effects on protein structure and function.

Example Problem: Describe the process of translation, highlighting the roles of mRNA, tRNA, and ribosomes.

Solution: mRNA carries the genetic code from DNA to the ribosome. tRNA molecules, each carrying a specific amino acid, bind to mRNA codons via their anticodons. The ribosome facilitates the formation of peptide bonds between amino acids, synthesizing a polypeptide chain based on the mRNA sequence.

IV. Evolutionary Mechanisms: How Populations Change

This section links genetics to evolution, exploring the mechanisms that drive changes in allele frequencies within populations.

Key Concepts:

• Hardy-Weinberg equilibrium: Understand the conditions required for a population to remain in Hardy-Weinberg equilibrium (no evolution): no mutation, random mating, no gene flow, large population size, no natural selection. Know how to use the Hardy-Weinberg equations (p + q = 1; p² + 2pq + q² = 1) to calculate allele and genotype frequencies.
• Genetic drift: Understand the impact of random fluctuations in allele frequencies, especially in small populations (founder effect, bottleneck effect).
• Gene flow: Analyze how the movement of alleles between populations affects allele frequencies.
• Mutation: Recognize mutation as the ultimate source of genetic variation.
• Natural selection: Master the concept of natural selection as the differential survival and reproduction of individuals based on their traits. Understand the different types of selection (directional, stabilizing, disruptive).
• Sexual selection: Recognize sexual selection as a form of natural selection driven by mate choice and competition for mates.

Example Problem: A population is in Hardy-Weinberg equilibrium for a gene with two alleles, A and a. The frequency of allele A is 0.7. Calculate the expected frequencies of the AA, Aa, and aa genotypes.

Solution:

• p (frequency of A) = 0.7
• q (frequency of a) = 1 - p = 0.3
• Frequency of AA = p² = (0.7)² = 0.49
• Frequency of Aa = 2pq = 2(0.7)(0.3) = 0.42
• Frequency of aa = q² = (0.3)² = 0.09

V. Speciation and Macroevolution: The Big Picture

This section explores the processes that lead to the formation of new species and the broader patterns of evolutionary change.

Key Concepts:

• Speciation: Understand the different modes of speciation (allopatric, sympatric).
• Reproductive isolation: Recognize the various mechanisms that prevent gene flow between populations (prezygotic barriers, postzygotic barriers).
• Phylogenetic trees: Interpret phylogenetic trees to understand evolutionary relationships between species.
• Evidence for evolution: Review the various lines of evidence supporting the theory of evolution (fossil record, biogeography, comparative anatomy, molecular biology).

Example Problem: Explain how allopatric speciation can occur.

Solution: Allopatric speciation occurs when a population is geographically separated into two or more isolated groups. Over time, these isolated populations may diverge genetically due to different selective pressures, genetic drift, and mutations. Eventually, they may become reproductively isolated, even if they come back into contact.

VI. Common Mistakes and Tips for Success

• Confusing genotype and phenotype: Remember that genotype refers to the genetic makeup, while phenotype refers to the observable traits.
• Misinterpreting Punnett squares: Practice constructing and interpreting Punnett squares for both monohybrid and dihybrid crosses.
• Failing to consider non-Mendelian inheritance patterns: Be prepared for questions involving incomplete dominance, codominance, pleiotropy, epistasis, and polygenic inheritance.
• Not understanding the Hardy-Weinberg principle: Master the Hardy-Weinberg equations and the conditions necessary for equilibrium.
• Misunderstanding the mechanisms of evolution: Clearly differentiate between genetic drift, gene flow, mutation, and natural selection.

VII. Frequently Asked Questions (FAQ)

Q: What are the most important concepts in AP Biology Unit 5?

A: Mendelian and non-Mendelian inheritance patterns, molecular genetics (DNA replication, transcription, translation), and the mechanisms of evolution (Hardy-Weinberg, genetic drift, gene flow, natural selection) are all crucial.

Q: How can I improve my understanding of Punnett squares?

A: Practice, practice, practice! Work through numerous examples, starting with simple monohybrid crosses and gradually progressing to more complex dihybrid and even trihybrid crosses.

Q: What resources can I use to study for the AP Biology exam?

A: Your textbook, class notes, online resources (Khan Academy, Bozeman Science), and practice tests are all excellent resources. Remember to focus on understanding the underlying concepts rather than just memorizing facts.

Q: How can I connect the concepts of genetics and evolution?

A: Remember that evolution is ultimately driven by changes in allele frequencies within populations. Genetic mechanisms such as mutation, genetic drift, gene flow, and natural selection are the forces that shape the genetic makeup of populations over time.

VIII. Conclusion

Mastering AP Biology Unit 5 requires a solid understanding of both Mendelian and non-Mendelian genetics, a grasp of molecular mechanisms, and a clear understanding of how these genetic principles underpin the process of evolution. By reviewing these key concepts and practicing problem-solving, you can confidently approach any question related to heredity and evolution on the AP Biology exam. Remember to focus on understanding the underlying principles rather than simply memorizing facts. Good luck!