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Transcript
Answer in writing: what is DNA? Where is yours? A very long macromolecules that contains your genetic material. It’s found in the nucleus of each one of your cells. Answer in writing: what is a gene? A segment of DNA which codes for a protein, which determines a trait. Evolution: a change in gene frequencies in a population between generations 4 Mechanisms of Evolution 1) 2) 3) 4) Gene flow (migration) Genetic drift (population bottlenecks) Mutation Natural selection Mechanisms of Evolution 1: Gene Flow (Migration) The exchange of genes between populations • decreases variation in population emigrated from • increases variation in population immigrated to • a significant force in human evolutionary history (no speciation) • accelerated travel/gene flow in recent years What was an example of gene flow in “the island of the colorblind?” Look at your video sheet and write “gene flow” next to it. Mechanisms of Evolution 2: Genetic Drift • occurs with isolation (absence of gene flow) and/or small population size • founder effect (e.g. first settlers on an island) Polydactyly (Ellis-van Creveld syndrome) • genetic bottlenecks (e.g. depopulation from catastrophe) What was an example of genetic drift in “the island of the colorblind?” Look at your video sheet and write “gene flow” next to it. “The Island of the Colorblind” as an example of (three) forces of evolution: • a bounded population • a mutation: achromatopsia gene • arrival of a European achromatopsia gene in the 18th century: gene flow (migration) • isolation: genetic drift • the typhoon: genetic drift (population bottleneck) • religious practices (encouraged inbreeding): genetic drift Forces of Evolution 3: Mutation Mutation is the source of new genetic variation: • actual change in a portion of the DNA of an organism. • some harmful, some beneficial, most have no effect and are passed unnoticed to offspring. • most common type of mutation is caused by copying errors during meiosis (sex cell division) • mutations do not cause evolution, they provide the material upon which the other evolutionary mechanisms act. Only way to introduce genetic variation from within a population. • Example: sickle cell anemia: mutation of recessive hemoglobin gene. Misshapen red blood cells cannot transport oxygen to tissues. Sickle-cell hemoglobin HbS HbS 1. Hemoglobin molecule Normal hemoglobin HbA HbA valine 2. Hemoglobin beta chain 3. Red blood cells Forces of Evolution 4: Natural Selection • mutation on its own has little effect on changing allele frequencies • but mutation + natural selection = rapid evolutionary change • sickle-cell carriers are protected from malaria Distribution of malaria Distribution of sickle-cell anemia Forces of Evolution 4: Natural Selection • sickle-cell carriers are protected from malaria •What is evolution? - a change in genes frequency in a population between generations - sickle-cell genes decline in frequency when malaria is not present - ex: decrease sickle-cell genes in African American population Forces of Evolution 4: Natural Selection • Natural selection: some individuals have genes that allow them to survive and reproduce more than other individuals. • These individuals have higher fitness (more offspring), and by producing more offspring, will pass on more genes to the next generation. • This increases the frequency of their genes in the population = natural selection! •Natural selection acts on the individual, although the population evolves.