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Understanding the Evolution of Populations: Key Concepts and Mechanisms

This lesson explores the history of life on Earth and the fundamental principles of evolution. It covers important definitions such as gene pool and relative frequency, and highlights sources of genetic variation, including mutations and gene shuffling. The text delves into single-gene and polygenic traits, detailing how natural selection influences these traits through directional, stabilizing, and disruptive selection. It introduces concepts like genetic drift and the Hardy-Weinberg principle, as well as classification systems and evolutionary taxonomy, illustrating these ideas through cladograms and phylogenetic relationships.

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Understanding the Evolution of Populations: Key Concepts and Mechanisms

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  1. EVOLUTION of POPULATIONS B-SC: Students will demonstrate an understanding of the history of life on Earth.

  2. defintions • gene pool: combined genetic information of all members of a particular population • relative frequency: # of times an allele occurs in a gene pool compared with the # of times other alleles occur

  3. In genetic terms, evolution is any change in the relative frequency of alleles in a population

  4. Sources of Genetic Variation • 2 main sources due to sexual reproduction (homologous chromosome independently assort in meiosis)

  5. Sources of Genetic Variation • MUTATIONS +/- changes phenotype +/- changes fitness

  6. 2. Gene Shuffling 2. Gene Shuffling • Cause of most heritable differences • Humans have 8.4 million different combinations of genes

  7. Single Gene Traits • When a single gene controls a phenotype • There are only 2 alleles: dominant & recessive

  8. Natural selection on single-gene traits can lead to changes in allele frequencies which leads to evolution

  9. Polygenic Traits • Controlled by 2 or more genes • Each gene has 2 or more alleles

  10. Natural Selection on Polygenic Traits • 3 different ways natural selection can affect phenotypes: • DIRECTIONAL SELECTION • STABILIZING SELECTION • DISRUPTIVE SELECTION

  11. DIRECTIONAL SELECTION • When individuals at either end of the bell-shaped curve have an advantage the curve moves in direction of advantage

  12. Stabilizing Selection • When individuals near the mean of the graph have advantage (higher fitness) the bell shape becomes taller

  13. Disruptive Selection • When individuals at both extremes have advantage (or middle has decreasing fitness)the middle decreases

  14. Genetic Drift • seen in small populations • may see a particular allele producing more offspring than would happen by chance • over time a series of chance occurrences can make an uncommon allele common

  15. Founder Effect • when small sampling of large population colonizes new habitat & allele frequencies not representative of original population

  16. Hardy-Weinberg Principle • states that allele frequencies in a population will remain constant unless 1 or more factors cause those frequencies to change • when allele frequencies remain constant population is said to be in genetic equilibrium

  17. 5 conditions necessary to maintain genetic equilibrium • Random Mating • Large Population • No Immigration or Emigration • No Mutations • No Natural Selection (all genotypes have same chance of survival)

  18. Hardy-Weinberg Equation

  19. CLASSIFICATION • Classification systems used to name organisms & to group them in a logical manner. • Linnaeus (Swedish botanist ) developed binomial nomenclature: 2 part name for every species (Genus species) • Man: Homo sapiens

  20. Evolutionary Classification TAXONOMY PHYLOGENY • discipline of classifying organisms & assigning each organism a universally accepted name • the study of evolutionary relationships among organisms

  21. Taxonomy Phyogeny

  22. Cladograms • diagram that shows evolutionary relationships among a group of organisms • an evolutionary tree of life

  23. Quick Lab page 453 Hand in for grading

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