3_NatSelectW11 - Evolution & Natural Selection •...

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Unformatted text preview: Evolution & Natural Selection • Evidence for Evolution – Species change over time – Species are related • Evolution and goals • Natural selection TurningPoint Clickers • To see channel of clicker press “Ch” button • Setting clicker to receiver channel – Press “Ch” button – Enter channel number – Important! Press and release “Ch” button again. – New channel should appear on LCD screen TurningPoint Clickers • To answer question – Wait for polling to start – Press the ONLY the number/letter of your answer – Green light if answer was received • LED lights – Red- response not received (prohibited sign appears) – Yellow blink- sending – Yellow or red single flash - polling not open I have used clickers before • A. Yes, here at UCLA • B. Yes, but only at another school • C. No ? TurningPoint Clickers: FAQ • How do I know if my answer was received? – The light should be green only after sending, the “prohibited’ sign should not appear – Be sure your clicker is on the right channel • I’m switching clickers (or borrowing someone else’s for the day, etc), is that a problem? – You must email me with the clicker serial number, your uid, and the lecture you are enrolled in. You cannot share with another student in either lecture of LS1 • After today no excuses. Any dead batteries, forgotten clickers, etc., will be part of the 6 days you can miss. Which observations about the fossil record would be consistent with a single special creation event, but not with evolution? • A. Overlap of older and newer forms across strata • B. All or most species, including extant species, occur in earliest layers, followed by loss of species only • C. Fossil species sometimes appear earlier or persist later in some areas but not others • D. A & B • E. B & C ? Transitional Forms: Whales • Fossils forms from hippo-like ancestor to whale Freeman, Fig 24.11 Transitional Forms • Anything may be a transitional form – Species change through time – Extreme shifts in habitat or form catch our attention • Transitional forms ... – Do not have lower fitness than ancestors – Do not show changes in all traits simultaneously or at the same rate • rate of change in traits ranges from slow to fast Transitional Forms Ancestor Changes in forehead, eye shape, mouth, length, legs, teeth, tail, neck, spines, color, eye color Descendant Transitional Forms Shared Ancestry: Phylogeny Bacteria • Phylogeny is the evolutionary relationship between species • Phylogenetic trees show that relationship • Geographic patterns can reflect phylogeny Freeman, Fig 24.6 Archaea Flowering plants Mosses Tapeworms Vertebrates Fungi Phylogeny & Geography • Phylogeny of Darwin’s mockingbirds (Genus Nesomimus) reflects geographic pattern N. parvulus (Santa Cruz) N. parvulus (Santiago) Genovesa Marchena N. parvulus (Marchena) Galápagos islands Santiago N. parvulus (Isabela) Santa Cruz Common ancestor N. trifasciatus (Floreana) N. melanotis (San Cristobal) N. parvulus (Genovesa) San Cristobal Isabela 50 km Floreana N. macdonaldi (Española) Mockingbird species from the Caribbean and Gulf of Mexico Freeman, Fig 24.6 Española Shared Ancestry: Homology • Homology – Similarity from shared (common) ancestry – Homologous traits • Three levels – Genetic • Example: ribosomal RNA genes – Developmental – Structural Shared Ancestry: Developmental Homology Freeman, Fig 24.8 Shared Ancestry: Structural Homology Freeman, Fig 24.9 Vestigial Traits • Humans – Appendix • Cecum in ancestor, aided in digestion – Coccyx (Tailbone) • Tail in ancestor, aided in balance – Wisdom Teeth • In ancestor, either replaced lost teeth or filled longer jaw – Goosebumps • In ancestor, fluffs fur for warmth Freeman, Fig 24.5 Vestigial Traits Evolution: Evidence of Change Through Time • Geology shows Earth is old • Most species have gone extinct • Fossil species frequently resemble extant species in same area • Transitional forms of fossils • Vestigial traits Evolution as Fact • What are these observations? – Most known in Darwin’s time – Elaborated on & further confirmed since • If species evolve then … – Species change over time – Species are related • Shared (Common) Ancestry Shared Ancestry: Geographic Relationships • Similar species occur in the same area – Mockingbirds in Galapagos (Darwin) – Marsupials in Australia – Lemurs in Madagascar • Species descended from common ancestor Geographic Relationships: The Wallace Line Darwin’s (and Wallace’s) Insight • Proposed natural selection (theory) as a process to explain evolution (observation/ fact) • Key components – – – – Organisms in a population vary in traits At least some traits are heritable More offspring will be born than can survive Survival not random, certain heritable traits promote survival. These traits will be favored by natural selection. “Differential Success” Heritable Variation A1 A1 A 1A 1 A1 A2 Light Dark A 1A 1 A 1A 2 A 1A 2 A1 A2 A 1A 2 A 1A 2 A 2A 2 A 2A 2 A 1A 1 A 2A 2 A2 A2 • Phenotype – Physical and physiological traits – Basis for selection • Genotype – Genetic makeup of organism – Alleles of organism • Alleles – Version of a genes – Diploid organisms have two alleles for every gene Heritable Variation • Allele A2 codes for dark pigment – Dominant: determines phenotype – A1A2 & A2A2 genotypes have black phenotype • Allele A1 is recessive – A1A1 individuals are white A 1A 1 A 1A 2 A 2A 2 A 1A 2 A 2A 2 A 1A 1 A 1A 2 A 1A 2 A 2A 2 A 1A 1 Frequency of A1 allele Start Frequency of A2 allele 0.5 (10 of 20 alleles present) 0.5 (10 of 20 alleles present) Differential Success A 1A 1 A 2A 2 • Birds find and eat black moths more easily A 1A 2 A 1A 1 Evolution via Natural Selection • Evolution is a change in allele frequencies in a population over time • Natural selection is when that change is from certain alleles favoring survival A 1A 1 A 1A 2 Frequency of A1 allele End A 2A 2 A 1A 1 Frequency of A2 allele 0.625 (5 of 8 alleles present) 0.375 (3 of 8 alleles present) Fitness and Adaptation • Fitness – Ability of individual to produce surviving young as compared to others in the population – Fitness is always in comparison to others, never absolute • Adaptation – Heritable trait that increases fitness – Created or maintained by natural selection Points to Remember • Traits must be heritable for evolution – Non-heritable traits acquired within an organism’s lifetime cannot be basis for evolution – Example: What we learn in class will not be genetically passed on However, the ability to learn is. • Natural Selection is not random – Example: Birds finding dark moths more easily than light • Other evolutionary mechanisms besides natural selection Points to Remember Bacteria Archaea Green algae Land plants Invertebrates Vertebrates Humans Vertebrates Invertebrates Land plants Green algae Fungi Bacteria Spontaneous generation • Evolution is not goal oriented – Both complexity and simplicity can be selected for – Example: Parasites are often selected for simplicity Fungi Evolution & “Goals” • Can we test the idea that evolution is goal oriented? • Prediction – If evolution is “goal oriented,” then the appearance of new beneficial traits should appear in response new environmental challenges – If evolution is NOT “goal oriented,” then the appearance of new traits should be random, and they may or not be beneficial Outbreaks of zombie-ism have occurred across the planet, thanks to the widespread release of the T-virus. If evolution is random, as opposed to goal oriented, then what pattern would you expect after several human generations (assume no change in mutation rate)? • A. Immunity to the T-virus would appear in some human populations but not others. Some populations would have widespread immunity, others little imunity • B. Immunity would appear in all populations at about the same rate Fluctuation Experiment-Luria and Delbrück • Plated bacteria from many cell cultures onto plates containing antibiotics, looked for resistant colonies • Hypothesis 1: Bacteria evolve resistance to antibiotics in response to exposure to antibiotics – Prediction: number of resistant colonies will be roughly the same for all cultures • Hypothesis 2: Bacterial resistance to antibiotics arises from random, non-directed mutations, followed by selection – Prediction: number of resistant cell colonies will be very variable (“fluctuating”) Apply Antibiotic Because # of resistant colonies is highly variable, or “fluctuating,” conclude that mutations are spontaneous, not in response to selection Apply Antibiotic Because # of resistant colonies is highly variable, or “fluctuating,” conclude that mutations are spontaneous, not in response to selection ...
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This note was uploaded on 06/03/2011 for the course LS 1 taught by Professor Thomas during the Spring '05 term at UCLA.

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