Summary of AP Biology Unit 7: Natural Selection
In this lecture, we covered Unit 7 on Natural Selection in great depth. The central theme of this unit is evolution, which is described as changes in allele frequencies or genetic codes within a population. We explored various mechanisms that drive these changes, notably natural selection and genetic drift, and discussed their implications on allele frequencies. We also covered the Hardy-Weinberg equilibrium, speciation, and phylogenetics to understand the evolutionary relationships and the formation of new species. Lastly, the lecture touched on mass extinctions and the origins of life, providing a historical context to evolutionary theory.
Detailed Notes
Evolution: Definition and Basic Idea
- Evolution is about the change in allele frequency or genetic code in a population.
- Illustrated with examples like bacteria developing resistance to antibiotics and changes in moth populations due to industrial melanism.
Natural Selection
- Natural selection is a mechanism by which evolution occurs and is not synonymous with evolution.
- It operates on the principle that certain traits become more common in a population due to differential reproductive success.
- Examples given included antibiotic resistance in bacteria and color changes in moth populations due to environmental changes.
Genetic Drift
- Genetic drift involves random changes in allele frequencies, especially significant in small populations.
- Founder effect and bottleneck effect: Two types of genetic drift that were explained focusing on how they cause significant genetic changes due to random sampling of alleles.
Gene Flow
- Refers to the transfer of genetic variation from one population to another, affecting allele frequencies.
Hardy-Weinberg Equilibrium
- The principle used to measure when a population is not evolving.
- Conditions for Hardy-Weinberg Equilibrium include large population size, no mutations, random mating, no gene flow, and no natural selection.
- Demonstrated using mathematical calculations to understand allele and genotype frequencies under certain conditions.
Speciation
- Covered the definition of speciation and the biological species concept, which includes the ability to interbreed and produce viable offspring.
- Allopatric vs. Sympatric Speciation: Defined and discussed with examples to illustrate different mechanisms of species formation due to geographical isolation and other factors.
Phylogenetics
- Explored the study of evolutionary relationships through phylogenetic trees which depict common ancestral links among species.
- Discussed different types of traits such as homologous, vestigial, and analogous structures to illustrate evolutionary concepts.
Mass Extinctions
- The concept of mass extinctions and their historical significance were briefly mentioned, highlighting major events like the Cretaceous-Paleogene extinction.
Origin of Life
- Touched on historical perspectives on the origin of life, starting from early Earth conditions to the development of life forms.
- Discussed experiments like the Miller-Urey that simulated early Earth conditions and demonstrated synthesis of organic molecules from inorganic substances.
Conclusion
This lecture provided an extensive overview of natural selection and evolutionary processes, linking genetic concepts to evolutionary outcomes and exploring complex topics like speciation and phylogeny to understand the development of life on Earth.