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SAT Subject Test Biology Review Evolution R. Guido, Instructor May-June 2013 Evolution

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SAT Subject Test Biology Review Evolution R. Guido, Instructor May-June 2013 Evolution SAT Subject Test Biology Review Evolution R. Guido, Instructor May-June 2013 Evolution Change in genes of a population over time Microevolution - change in 1 population over generations Macroevolution - speciation or changes that produce an entirely new species Population - all members of a single species living in a specific area Evidence of Evolution 1. Fossil record 2. Comparative anatomy 3. Comparative biochemistry 4.Comparative embryology 5. Molecular biology 6. Biogeography Fossil Record 99% all organisms that ever lived have become extinct Prokaryotic cells are the oldest fossils Earth is approx. 4.6 billion years old, based on radioactive dating & half-life Transitional fossils Link older extinct fossils to modern species E.g. Archaeopteryx - fossil that is both reptile & bird Comparative Anatomy Organisms having similar anatomical features are related to each other & share a common ancestor: 1. Homologous structures Same structure but different function E.g. Wing of a bat, fin a whale, arm of a human 2. Analogous structures Different structure but same function Reflects an adaptation of different species to the same environment However, NOT evident of a common ancestry E.g. Wing of a bat, wing of a fly 3. Vestigial structures Evidence that animals have evolved E.g. Human appendix was once useful based on the diet of prehistoric humans Comparative Biochemistry The more closely organisms are related, the more similar their biochemistry E.g. Insulin of pig & human Comparative Embryology Closely related organisms go through similar stages of embryonic development Stages appear so similar that it is difficult to determine which organism is developing Molecular Biology Aerobic organisms contain a polypeptide called cytochrome c, needed to carry out cell respiration The amino acid sequence of this molecule is similar among closely related organisms Biogeography Theory of Continental Drift Continents were locked together approx 250 million years ago "Supercontinent" called Pangaea Slowly separated over the course of 150 million years Fossil evidence confirms marsupials (e.g. Kangaroos) migrated from land of South America to Antarctica before settling in Australia Lamarck Theory of Inheritance of Acquired Characteristics Stated that individual organisms changed in response to their environment E.g. Giraffe developed a long neck due to stretching for leaves high on the Acacia tree The stretching was an acquired trait that was passed on to offspring Theory of Use & Disuse The more an organ or structure is used, the more developed it will become in future offspring Darwin Theory of Natural Selection 1.Overpopulation - Populations tend to grow exponentially & exceed their resources 2.Struggle for existence - organisms compete for limited resources 3.Variation - unequal ability of certain organisms to survive long enough to reproduce 4.Survival if the Fittest - only those individuals best adapted tot he environment will survive, reproduce, & pass on those traits to their offspring 5.Speciation - Evolution occurs as an accumulation of advantageous traits in a given population Note: Source of Variation was not well understood until Mendel proposed his theories of Genetics in the late 1800's & DeVries described mutations in the early 1900's Process alters the frequencyNatural of inherited traitsSelection in a population by the following mechanisms: 1.Stabilizing Selection Eliminates extreme traits & favors the "middle ground" or more common forms Mutants are weeded out E.g.: human birth weight is favored to be in the middle at 7.5lbs or between 6 & 9 lbs 2. Disruptive (Diversifying) Selection Favors extreme types in a population at the expense of the middle ground May result in the formation of a new species E.g: 2 colors of shells in snails 3. Directional Selection Change in environment induces 1 phenotype to replace another E.g: Industrial Melanism - the Peppered Moth Sources of Darwin's Variations 1. Mutation Changes in genetic material Agent of Evolution 2. Genetic Drift Change in the gene pool due to chance Types A.Bottleneck Effect Natural disasters result in loss of genetic variation due to decrease in population size Result is a smaller population with certain alleles either under-represented or over-represented compared with the original population B Founder Effect When a small population breaks away from a larger one to a new area Again, certain alleles may be under- or over-represented 3. Gene Flow Movement of alleles into or out of population Hardy-Weinberg Equilibrium Theory that describes a stable, non-evolving population where allelic frequencies do not change Criteria for a population to remain in Hardy-Weinberg Equilibrium: 1.Population must be large - any subtle changes in alleles will not impact on overall allelic frequency 2.No migration - population must be isolated from others 3.No mutations - no changes in genes 4.Mating must be random - if mating is selective, then most fit will have a reproductive advantage and initiate evolution of population 5.No natural selection - no changes in allelic frequencies of gene pool Hardy-Weinberg Equation Used to calculate frequencies of alleles in population p2 + 2pq + q2 -Or- p + q = 1 where, p = dominant allele q = recessive allele p2 = homozygous dominant individuals 2pq = heterozygous dominant individuals q2 = homozygous recessive individuals Isolation & Speciation Isolated populations: Subject to different selective pressures in their environments As a result, they may accumulate enough changes to become a new species Forms of Isolation 1. Geographic isolation - occurs when species become separated 2. Polyploidy - type of mutation that results in extra sets of chromosomes 3. Habitat isolation - when 2 organisms live in the same area but rarely encounter each other, e.g. 2 species of snake, 1 lives in water, the other on land 4.Behavioral isolation - when 2 animals become isolated because 1 undergoes a change in behavior 5. Temporal isolation - different plants of 1 species living in same area may separate into 2 populations due to blooming at different time periods 6. Reproductive isolation - closely related species cannot mate due to anatomical differences, e.g. Large & small dog breeds Patterns of Evolution How species evolve is categorized into 5 patterns: 1. Divergent evolution - when population becomes isolated from rest of species & begins to evolve into its own species due to selective pressures from environment, i.e. species A & species B evolving from a single common ancestor 2. Convergent evolution - when unrelated species occupy same environment, exhibit similar adaptations, e.g. Whales & Sharks 3. Parallel evolution - 2 related species making similar adaptations in different regions e.g. North American wolf & Tasmanian wolf 4. Coevolution - set of adaptations between 2 interacting species, e.g. Pollinators & plants, predator & prey 5. Adaptive radiation - evolution of many species from a single common ancestor, e.g. Darwin's finches - 14 different species occupying a different ecological niche Theories about Evolution 1. Gradualism Organisms descend from a common ancestor slowly over time Accumulation of small changes into a new species Scientists generally don't accept theory due to lack of evidence in fossil record 2. Punctuated Equilibrium New species appear suddenly after long periods of no change Generally accepted by scientists who believe that ancestral species become extinct and are replaced by new species Heterotroph Hypothesis Earth's age is approx. 4.6 billion years old Ancient atmosphere made of: Methane Ammonia Water vapor Free nitrogen No free oxygen Heat, lightening, UV. Radiation provided energy for chemical reactions to give rise to the first cell Hypothesis states that 1st cells were anaerobic heterotrophic prokaryotes that evolved approx. 3.5 billion years ago Absorbed organic molecules from environment Heterotroph Hypothesis Eukaryotic cells evolved from prokaryotes about 1.5 billion years ago - possessed nucleus, membrane-bound organelles Endosymbiotic theory - describes how small bacteria took up residence inside large prokaryotic cells & performed functions in a symbiotic relationship, leading to formation of organelles Heterotroph Hypothesis 1st multicellular animal appeared approx 565 million years ago Within 40 million years, the phyla for all animals evolved - Cambrian era explosion Characteristics enabled animals to move from water to land: Lungs Skin Limbs Internal fertilization Hard, external shell Characteristics enabled plants to move from water to land: Roots Supporting cells to capture light Vascular tissue for transport of water, minerals Waxy cuticle to protect leaves Seeds Evolution of Mammals Mammals appeared approx 210 million yrs ago Primates - apes appeared about 25 million yrs ago Humans & apes co-evolved from a common ancestor approx 10 million yrs ago Human ancestors arose first in Africa Homo sapiens, modern human, arose approx 150,000 yrs ago.
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