Positional information in animal embryo prompts cells

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positional information in animal embryo => prompts cells to develop into structures appropriate for a particular location Mutations such as duplications can result in various body parts. *****EVOLUTION IS NOT GOAL ORIENTED!******* IG Lecture Outline 22-6
Chapter 26: Biological Diversity Geological events that alter environments change the course of biological history. (glaciers-lakes, speciation, man, oxygen, etc.) Fortunately, each organism alive today carries traces of its evolutionary history in its molecules, metabolism, and anatomy. 26.1 The Origin of Life Hypothetical scenario with four main stages: 1. abiotic synthesis of small organic molecules (monomers) 2. monomers into polymers 3. packaging into protobionts (membrane covered clusters that maintained a distinct internal chemistry) 4. self-replicating molecules Earth (and solar system) formed about 4.6 billion years ago. Oldest rocks on surface => 3.8 billion years old . Early atmosphere => reducing, thick with water vapor , nitrogen and oxides , carbon dioxide , methane , ammonia, H, hydrogen sulfide As Earth cooled, water vapor condensed into oceans and much H was lost into space. High radiation (young sun, no ozone), lightning Oparin and Haldane => early Earth could have formed organic from inorganic => oceans a primitive soup. Miller and Urey ( 1953) tested above hypothesis => discharged sparks in an “atmosphere” of gases and water vapor Result: variety of amino acids and other organic molecules (so they can form in a reducing atmosphere) New evidence: probably formed near deep-sea vents Extraterrestrial sources? Life on Mars? Life on Europa? Laboratory simulations => produced organic polymers (hot sand) => monomers splashed onto fresh lava Lab experiments => protobionts can form by self-assembly ex. lipids + other organic + water = liposomes (some life properties) RNA may have been the first genetic material. Reason: Ribozymes (RNA catalysts). Some remove own introns, some modify tRNA to fully function, others synthesize new RNA polymers. Occasional copying errors create mutations (different shape, different function); natural selection screens these mutations for the most stable or the best at self-replication; eventually DNA resulted (more stable, less errors). RNA became intermediates. 26.2 Introduction to the History of Life The relative sequence of fossils in rock strata tells us the order in which the fossils were formed, but it does not tell us their ages. Methods for obtaining absolute dates for fossils: IG Lecture Outline 22-7
1. radiometric dating => based on fixed rate of decay of radioactive isotopes that accumulated while the organisms were alive half-life => years it takes for 50% of the original sample to decay ex. carbon-14 accumulates until death, then decays to nitrogen-14, ratio is measured to determine age (half-life of 5,730 years-up to about 75,000 years old) potassium-40 for volcanic rock 2. Magnetism of rocks => Earth’s poles reversed repeatedly geologic record => history of life on Earth => see Table 26.1 (do not need to know it) mass extinctions => destroyed the majority of species on Earth Permian (volcanic eruptions-global warming); Cretaceous (

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