ap biology unit 5 notes

3 min read 01-02-2025

Unit 5 of AP Biology delves into the fascinating world of genetics and evolution, exploring how genetic variation arises, how it's inherited, and how it drives the evolution of populations over time. This comprehensive guide provides a detailed overview, hitting key concepts and offering strategies for mastering this crucial unit.

I. Mendel and the Gene Idea

This section revisits the foundational work of Gregor Mendel, laying the groundwork for understanding inheritance patterns.

A. Mendel's Laws:

Law of Segregation: Each gene has two alleles, and these alleles segregate (separate) during gamete formation. Each gamete receives only one allele.
Law of Independent Assortment: Alleles for different genes segregate independently of each other during gamete formation. This is true for genes on different chromosomes, but not always for genes located close together on the same chromosome (linked genes).

B. Types of Inheritance:

Complete Dominance: One allele completely masks the expression of the other.
Incomplete Dominance: Heterozygotes show a phenotype intermediate between the two homozygous phenotypes (e.g., pink flowers from red and white parents).
Codominance: Both alleles are fully expressed in heterozygotes (e.g., AB blood type).
Multiple Alleles: More than two alleles exist for a particular gene (e.g., ABO blood type).
Pleiotropy: One gene affects multiple phenotypic characteristics.
Epistasis: The expression of one gene affects the expression of another gene.
Polygenic Inheritance: Multiple genes contribute to a single phenotypic characteristic (e.g., human height).

II. Extensions of Mendelian Genetics

This section explores deviations from simple Mendelian inheritance patterns.

A. Sex-linked Genes:

Genes located on sex chromosomes (X and Y in humans). X-linked recessive traits are more common in males because they only need one copy of the recessive allele to express the trait.

B. Linked Genes and Recombination:

Genes located close together on the same chromosome tend to be inherited together. However, crossing over during meiosis can lead to recombination of linked genes, producing recombinant gametes with new combinations of alleles. The frequency of recombination is related to the distance between genes on the chromosome.

C. Genetic Mapping:

Using recombination frequencies to create a genetic map showing the relative positions of genes on a chromosome.

III. Molecular Basis of Inheritance

This section dives into the molecular mechanisms underlying inheritance.

A. DNA Structure and Replication:

The double helix structure of DNA and the process of DNA replication, ensuring the accurate transmission of genetic information.

B. Gene Expression:

The process by which genetic information encoded in DNA is transcribed into RNA and then translated into protein. This includes transcription, RNA processing (in eukaryotes), and translation.

C. Mutations:

Changes in the DNA sequence that can lead to altered gene function or expression. These can be point mutations (substitutions, insertions, deletions) or chromosomal mutations (deletions, duplications, inversions, translocations).

IV. Population Genetics

This section shifts the focus from individual organisms to populations and explores how genetic variation changes across generations.

A. Hardy-Weinberg Equilibrium:

A model that describes the conditions under which allele and genotype frequencies in a population remain constant from generation to generation. Deviations from Hardy-Weinberg equilibrium indicate that evolutionary forces are acting on the population.

B. Evolutionary Mechanisms:

Natural Selection: Differential survival and reproduction of individuals based on their traits.
Genetic Drift: Random fluctuations in allele frequencies, particularly pronounced in small populations. Includes the bottleneck effect and founder effect.
Gene Flow: Movement of alleles between populations.
Mutation: Introduces new alleles into the population.

V. Speciation and Macroevolution

This section examines how new species arise and how major evolutionary changes occur over long time scales.

A. Speciation:

The process by which new species arise, often through reproductive isolation mechanisms (pre-zygotic and post-zygotic barriers).

B. Macroevolution:

Large-scale evolutionary changes, including the origin of new taxonomic groups and major evolutionary trends.

This detailed outline covers the major topics within AP Biology Unit 5. Remember to consult your textbook, class notes, and practice problems to fully grasp the concepts and prepare effectively for the AP exam. Good luck!