Lecture 8: Evolution and Natural Selection PDF

Lecture 8: Evolution and Natural Selection ©JoAnna Wendel  Reminder Quiz 3 due Friday by 11:59pm UM Learn “Assignments” Today’s Objectives Introduction to the Theory of Evolution by Natural Selection Learn the relationship between genetics and variation in a popula...

Lecture 8: Evolution and Natural Selection ©JoAnna Wendel  Reminder Quiz 3 due Friday by 11:59pm UM Learn “Assignments” Today’s Objectives Introduction to the Theory of Evolution by Natural Selection Learn the relationship between genetics and variation in a population Natural History Museum Themes Earth is a dynamic planet that has changed continuously since its origin some 4.6 billion years ago Three themes run throughout Earth’s history: Plate tectonics Geologic time Evolution What is Evolution? Changes in heritable traits in populations (groups of individuals of the same species that live together) over time “Descent with modification” Can result in new species Carl Buell Mechanism? Darwin and Wallace on Evolution 1859: jointly published their views on evolution and proposed natural selection as the mechanism for evolutionary change Both observed variation in natural populations Independently came up with the idea that natural processes select favorable individuals from populations for survival Images: commons.wikimedia.org; Darwin (1837: “Notebook B”) Darwin and the Galápagos Islands Image: Stanley (2009) Galapagos tortoises have two very different shapes, each adapted for different feeding habits needed on low, arid islands versus high, lusher islands. Fig 7.1 Galápagos Island Finches Fig 7.2  What is the Significance of Natural Selection? Natural selection is a mechanism for evolution Organisms possess heritable variations Some variations are more favorable than others in certain environments Not all young survive to maturity Individuals with favorable variations are more likely to survive to reproduce and pass on their favorable variations. "Survival of the fittest“ Involves inheritable variations leading to differential reproductive success Co Fig 7.4 industrializationpolled moredar as areas Darwinian natural selection! Artificial Selection Selective breeding of domestic animals and plants → artificial selection Fig 7.3 Images: commons.wikimedia.org  Mendel and the Birth of Genetics 1860s: Mendel’s breeding experiments with garden peas showed how variation is maintained and passed on Traits are controlled by a pair of factors (genes) Alleles: alternate forms of genes that control the same trait Genes that control traits do not blend during inheritance Genes are not lost even though not expressed in every generation Dominant and recessive alleles Fig 7.5 Mendel and the Birth of Genetics Images: commons.wikimedia.org  Image: Stanley (2009) Image: National Human Genome Context of a gene: located within a strand of eukaryotic DNA Complete set of human chromosomes (made of organized into the paired chromatids of a chromosome DNA, which is split into regions called genes, which Basic unit of heredity have different versions called alleles Expressed as traits or held in a recessive state (no expression)  Meiosis *Pollen Mitosis fertilizes ovule in plants Reshuffling of genes from generation to generation; creates variations that natural selection works on Production of gametes (sex cells: sperm & eggs / Used for almost all cell division needs pollen & ovules) Fig 7.6 Adds cells during development Goal: produce daughter cells with exactly half as Replaces worn-out cells during life many chromosomes as the starting cell Goal: produce daughter cells identical to starting cells What brings about new variations? Mutations Changes in chromosomes or genes: changes in the hereditary information Chromosomal mutations affect a large segment of the chromosome Point mutations affect a single gene May be harmful, beneficial, or have no effect Caused by mutagens: chemicals, radiation, or temperature extremes Or can be spontaneous  Variation Sexual reproduction and mutations account for most variation in populations Genetic drift: a random change in a gene in a population is due to chance Affects small populations more than large ©New York Times The Modern View of Evolution Modern synthesis or neo-Darwinism view Early 20th century: genetics was included in evolutionary thinking Natural selection was reaffirmed Ideas of genetic drift emerged Importance of mutations were realized Mentimeter review