EVOLUTION/POPULATION GENETICS CH SOME INFLUENCES ON DARWINS THOUGHT James Hutton Charles Lyell Jean-Baptiste Lamarck Thomas Malthus Alfred Russell Wallace : Contributors to Darwins thinking included: Charles Lyell uniformatarianism Georges Cuvier species extinction (Catastrophism) Thomas Malthus struggle for existence (resources) : Contributors to Darwins thinking included: James Hutton - Gradualism Jean Baptiste Lamarck Inheritance of acquired Characteristics and Law of Use and Disuse Alfred Russell Wallace organisms evolved from common ancestors Huttons Theory of Geological Change James Hutton, 1795, Scottish geologist Studied invertebrate fossils in Paris Museum Described The Geological Forces That Have Changed Life on Earth Over Millions of Years (erosion, earthquakes, volcanoes) Huttons Theory of Geological Change Changes in Earths crust is due to slow continuous processes Idea Known as Gradualism Charles Lyell ( ) Proposed theory of Uniformitarianism Geological processes occur at uniform rates building & wearing down Earths crust Proposed that the Earth was millions of years instead of a few thousand years old Principles of Geology Published by Lyell Just Before The Beagle Set Sail & read by Darwin Explained Geological Processes That Shaped The Earth Helped Darwin Understand Sea Shells In The Andes Mountains At 12,000+ Feet Expanded Earths Age Lamarcks Theory of Evolution Jean-Baptiste Lamarck, 1809 One Of First Scientists To Understand That Change Occurs Over Time Stated that Changes Are Adaptations To Environment acquired in an organisms lifetime Said acquired changes were passed to offspring Lamarcks Theory of Evolution Idea called Law of Use and Disuse If a body part were used, it got stronger If body part NOT used, it deteriorated Lamarcks Theory of Evolution Inheritance Of Acquired Traits Traits Acquired During Ones Lifetime Would Be Passed To Offspring Clipped ears of dogs could be passed to offspring! Lamarcks Mistakes Lamarck Did NOT Know how traits were inherited (Traits are passed through genes) Genes Are NOT Changed By Activities In Life Change Through Mutation Occurs Before An Organism Is Born Population Growth Thomas Malthus, 1798 Economist Observed Babies Being Born Faster Than People Were Dying Population size limited by resources such as the Food Supply The Struggle for Existence Malthus Influence: High Birth Rates & Limited Resources Would Force Life & Death Competition Each Species Struggles For: Food Living Space Mates Population Growth Malthus Reasoned That If The Human Population Continued To Grow Unchecked, Sooner or Later There Would Be Insufficient Living Space & Food For Everyone Death Rate Will Increase To Balance Population size & Food Supply Population Growth Darwin Realized Malthuss Principles Were Visible In Nature Plants & Animals Produce Far More Offspring Than Can Be Supported Most Die If They Didnt Earth Would Be Overrun Wallaces Contribution Alfred Russell Wallace Independently came to same Conclusion as Darwin that species changed over time because of their struggle for existence When Darwin read Wallaces essay, he knew he had to publish his findings Darwin's Theory 1.Individual Organisms In Nature Differ From One Another. Some Of This Variation Is Inherited 2. Organisms In Nature Produce More Offspring Than Can Survive, And Many Of These Offspring Do not Reproduce Darwin's Theory 3.Because More Organisms Are Produced Than Can Survive, Members Of Each Species Must Compete For Limited Resources 4.Because Each Organism Is Unique, Each Has Different Advantages & Disadvantages In The Struggle For Existence Darwin's Theory 5.Individuals Best Suited To Their Environment Survive & Reproduce Successfully Passing Their Traits To Their Offspring. 6.Species Change Over Time. Over Long Periods, Natural Selection Causes Changes That May Eventually Lead To New Species Darwin's Theory 7.Species Alive Today Have Descended With Modifications From Species That Lived In The Past 8.All Organisms On Earth Are United Into A Single Tree Of Life By Common Descent Concept Map Section 15-3 includes Evidence of Evolution Physical remains of organisms Common ancestral species Similar genes which is composed ofwhich indicateswhich implies The fossil record Geographic distribution of living species Homologous body structures Similarities in early development Fossil Record Old remains of the past Earth is Billions of Years Old Fossils In Different Layers of Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time Homologous Structures Beaver NORTH AMERICA Muskrat Capybara SOUTH AMERICA Coypu Geographic Distribution of Living Species Section 15-3 Beaver Muskrat Beaver and Muskrat Coypu Capybara Coypu and Capybara TurtleAlligatorBirdMammal Ancient lobe-finned fish HOMOLOGOUS STRUCTURES Section 15-3 In evolutionary biology, homology refers to any similarity between characteristics of organisms that is due to their shared ancestry. The word homologous derives from the ancient Greek , 'to agree'. Evidence for Evolution - Comparative Embryology Similarities In Embryonic Development Homologous Body Structures Not All Serve Important Functions Vestigial Organs- no longer serve a function Appendix In Man Legs On Skinks Similarities in DNA Sequence Evolutionary Time Scales Long time scale events that create and destroy species. Macroevolution: Long time scale events that create and destroy species. Microevolution: Short time scale events (generation- to-generation) that change the genotypes and phenotypes of populations Evolutionary Time Scales Sample Population 48% heterozygous black 36% homozygous brown 16% homozygous black Frequency of Alleles allele for brown fur allele for black fur VARIATION & GENE POOLS Section 16-1 Gene pool Relative frequency # of times an allele occurs in a gene pool, compared w/ the # of times other alleles for the same gene occur MUTATION THE ULTIMATE SOURCE OF GENETIC VARIATION!!!!!! Frequency of Phenotype (%) Widows peakNo widows peak Phenotype Phenotypes for Single-Gene Trait - # of phenotypes a given trait has is determined by how many genes control the trait Section 16-1 * Controlled by a single gene that has 2 alleles leads to 2 distinct phenotypes Frequency of Phenotype Phenotype (height) Generic Bell Curve for Polygenic Trait: many possible genotypes and phenotypes Section 16-1 *Controlle d by 2/ more genes (2/ more alleles) Directional Selection Food becomes scarce. Key Low mortality, high fitness High mortality, low fitness NATURAL SELECTION ON POLYGENIC TRAITS: 3 MODELS Section 16-2 Favors traits at 1 extreme of a range of traits Key Percentage of Population Birth Weight Selection against both extremes keep curve narrow and in same place. Graph of Stabilizing Selection Section 16-2 Low mortality, high fitness High mortality, low fitness Stabilizing Selection Individuals with the most common trait are most adapted, while individuals who differ from the norm are poorly adapted. Stabilizing Selection Natural selection acts in opposite directions *** Heterozygote Advantage- ind who is heterozygous for a particular gene has a greater fitness than a homozygous indfitness EX: Distribution of sickle-cell allele coincides with the occurrence of malaria SS Normal hemoglobin ss Sicke-cell disease Ss- codominance (protects against malaria) Disruptive Selection Largest and smallest seeds become more common. Number of Birds in Population Beak Size Population splits into two subgroups specializing in different seeds. Beak Size Graph of Disruptive Selection Number of Birds in Population Key Low mortality, high fitness High mortality, low fitness Section 16-2 When both extreme phenotypes are favored by natural selection Acts in opposite directions GENTIC DRIFT A RANDOM CHANGE IN ALLELE FREQUENCY IN SMALL POPULATIONS, INDIVIDUALS THAT CARRY A PARTICULAR ALLELE MAY LEAVE MORE DESCENDANTS THAN OTHER INDIVIDUALS, JUST BY CHANCE. OVER TIME, A SERIES OF CHANCE OCCURRENCES OF THIS TYPE CAN CAUSE AN ALLELE TO BECOME COMMON IN A POPULATION. FOUNDER EFFECT: A SITUATION IN WHICH ALLELE FREQUENCIES CHANGE AS A RESULT OF THE MIGRATION OF A SMALL SUBGROUP OF A POPULATION. Sample of Original Population Founding Population A Founding Population B Descendants Genetic Drift Section 16-2 In small populations, an allele can become more or less common by chance (explain how allele frequencies can fluctuate unpredictably from 1 gen to the next) Sample of Original Population Founding Population A Founding Population B Descendants Genetic Drift Section 16-2 FOUNDER EFFECT: 2 small groups from a large, diverse population could produce new populations that differ from the original population Sample of Original Population Founding Population A Founding Population B Descendants Genetic Drift Section 16-2 EVOLUTION VERSUS GENETIC EQUILIBRIUM HARDY-WEINBERG PRINCIPLE: ALLELE FREQUENCIES IN A POPULATION WILL REMAIN CONSTANT AS LONG AS FIVE CONDITIONS (FACTORS) REMAIN CONSTANT. GENETIC EQUILIBRIUM IS REACHED. (IS THE POPULATION EVOLVING?) 5 CONDITIONS REQUIRED TO MAINTAIN GENETIC EQUIIBRIUM 1.RANDOM MATING - Select mates w/o bias 2.LARGE POPULATION - Genetic drift does not affect large pops 3. NO MOVEMENT INTO OR OUT OF THE POPULATION - no intro of new allele 4. NO MUTATION - no new allele introduced 5.NO NATURAL SELECTION - No phenotype can have selective advantage DOES THIS EVER HAPPEN????? In 1908, Hardy and Weinberg independently demonstrated that DOMINANT ALLELES DO NOT REPLACE RECESSIVE ALLELES IN A POPULATION! HARDY-WEINBERG EQUATION You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: The frequency of the "aa" genotype. The frequency of the "a" allele. The frequency of the "A" allele. The frequencies of the genotypes "AA" and "Aa." The frequencies of the two possible phenotypes if "A" is completely dominant over "a." FREQUENCY OF aa GENOTYPE: 36% (GIVEN) FREQUENCY OF a ALLELE:The frequency of aa is 36%, which means that q 2 = 0.36, by definition. If q 2 = 0.36, then q = 0.6, again by definition. Since q equals the frequency of the a allele, then the frequency is 60%. The frequency of the "A" allele. Answer: Since q = 0.6, and p + q = 1, then p = 0.4; the frequency of A is by definition equal to p, so the answer is 40%. The frequencies of the genotypes "AA" and "Aa." Answer: The frequency of AA is equal to p 2, and the frequency of Aa is equal to 2pq. So, using the information above, the frequency of AA is 16% (i.e. p 2 is 0.4 x 0.4 = 0.16) and Aa is 48% (2pq = 2 x 0.4 x 0.6 = 0.48). The frequencies of the two possible phenotypes if "A" is completely dominant over "a." Answers: Because "A" is totally dominate over "a", the dominant phenotype will show if either the homozygous "AA" or heterozygous "Aa" genotypes occur. The recessive phenotype is controlled by the homozygous aa genotype. Therefore, the frequency of the dominant phenotype equals the sum of the frequencies of AA and Aa, and the recessive phenotype is simply the frequency of aa. Therefore, the dominant frequency is 64% and, in the first part of this question above, you have already shown that the recessive frequency is 36%. AS NEW SPECIES EVOLVE (SPECIATION), POPULATIONS BECOME REPRODUCTIVELY ISOLATED FROM EACH OTHER. Section 16-3 results from which include produced by which result in Reproductive Isolation Isolating mechanisms Behavioral isolationTemporal isolation Geographic isolation Behavioral differencesDifferent mating times Physical separation Independently evolving populations Formation of new species Section 17-4 Flowchart that are can undergo inunder formin Species Unrelated Related Inter- relationshiops Similar environments Intense environmental pressure Small populations Different environments Coevolution Convergent evolution Extinction Punctuated equilibrium Adaptive radiation Types of Reproductive Isolation A)Behavioral- occurs when pops have different courtship rituals. B)Geographic- occurs when pops are separated by geographic barriers. Ex: mountains & rivers C) Temporal- occurs when pops reproduce at different times. Ex: orchids in the rainforest a.Divergent evolution when 2/ more species originate from a common ancestor Ex: flipper of whale and limb of human b. Convergent evolution process by which unrelated organisms come to resemble each other Ex: torpedo shape of shark and penguin/ wing of insect and bat c. Coevolution process by which 2 species evolve in response to changes in each other over time