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Health Sciences
HSCI 100
Nienke Van Houten

CH22:EVOLUTION&HERITAGE Origin of life through chemical evolution A. Primitive atmosphere contained gases (h2o, co2, n2) that escaped from volcanoes. As water vapor cooled, some gases were washed into oceans by rain B. Availability of energy from volcanic eruption and lightning allowed gases to form small organic molecules (nucleotides/amino) C. Small organic molecules could have joined to form proteins & nucleic acids (which became incorporated into membrane bound spheres) - Spheres become the first cells (protocells) later protocells became true cells that could reproduce Inorganic molecules form small organic molecules  small organic molecules join to form larger organic molecules  large organic molecules, possibly including RNA/small proteins aggregate within droplets  droplets eventually form true prokaryotic cells  eukaryotic cells arise  multicellular eukaryotic organisms such as plants and animals arise. BIOLOGICAL EVOLUTION – change in population/species & their alleles over time - Living things descended from a common ancestor and thus, have common chemistry - Living things adapt to their environment - Natural selection operates on reproductive fitness and success - Next generation is a result of existing variatiability, new mutations, selection and genetic drift Adaptation: a characteristic that makes an organism survive and reproduce in its own environment SCALE OF EVOLUTIONARY CHANGE: MICROEVOLUTION: changes in frequency of certain alleles relative to others within gene pool of population Population: group of individuals of same species living in particular area gene pool: all alleles of all genes of all individuals in a population mutation: change in nucleotide sequence of DNA GENETIC DRIFT - allele frequencies within population change randomly because of chance alone - Bottleneck effect: population experiences dramatic decrease in size and few individuals remaining contribute to gene pool where genetic makeup may not be representative of original population - Founder effect: few individuals leave population to isolated place, genetic makeup of colonizing individuals not representative of full gene pool of population they left GENE FLOW – individuals move into&out of populations, as individuals come and go they carry unique sets of genes o Occurs if individuals successfully interbreed, adding to gene pool - Species: population/group of populations whose members are capable of successful interbreeding (under natural conditions & produce fertile offspring) - Speciation: multiple species of individuals forms when separated for very long (E.g. land frogs, water frogs) 1 MUTATIONS – rare changes in DNA of genes - Mutations produce new alleles in gene pool and introduced to population, then acted on by natural selection NATURAL SELECTION – some individuals have more surviving offspring than others because their particular inherited characteristics makes them better suited to their local enviro - Fitness: compare number of reproductively viable offspring among individuals Darwin’s theory based on: 1. Variation – there is heritable variation for selection to act upon 2. Competition – resources (food, mates, shelter) are finite & therefore limited & thus competition for survival & reproduction 3. Adaptation – as long as the environment remains unchanged & some heritable variants provide an advantage the subsequent generations will see an increase in individuals with those traits. (transformation of population toward better fitness in their environment) MACROEVOLUTION: large-scale evolutionary change, changes in groups of species SCIENTIFIC NAMES - species-genus-family-order-class-subphylum-phylum-kingdom-domain PHYLOGENETIC TREE – branching diagrams used by scientists to depict hypotheses about evolutionary relationships among species, groups of species (character matrix) EVIDENCE OF EVOLUTION: Fossils in the fossil record - Fossils = mineralized remains of organisms that lived in the past - Fossils form in strata (layers) via sedimentation - Allow us to trace descent of a particular group - Transnational fossils = characteristics of 2 diff groups o Dinosaurs == birds - From the fossil records: o Life progressed from simple to more complex o Prokaryotes are the first life forms seen in the fossil records followed by unicellular eukaryotes and then multicellular eukaryotes o Fishes evolved before terrestrial plants & animals o Amphibians preceded reptiles & reptiles preceded birds o Dinosaurs are directly linked to birds - Limitations: relatively are, unlikely they wouldn’t be destroyed before being found, biased sampling of past life Biogeographical evidence – study of geographic distribution of organisms - Diff islands = diff finches 2 - Each species thought to come from common ancestor from mainland - Adapted beak shapes based on diet/available food - Classic example of natural selection Anatomical evidence o Homologous structures: similar structures inherited from common ancestors o Vestigial structures: anatomical features that are developed in one set of organisms but reduced in another  Pelvic girdle in wheel, human tailbone, wings on ostrich o Convergent evolution: independent groups evolved because of similar ecological roles & selection pressures o Structures similar b/c of convergent evolution = Analogous structures: same function, di
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