Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The Selfish Gene wikipedia , lookup
Hologenome theory of evolution wikipedia , lookup
Sexual selection wikipedia , lookup
Theistic evolution wikipedia , lookup
Inclusive fitness wikipedia , lookup
The Descent of Man, and Selection in Relation to Sex wikipedia , lookup
Saltation (biology) wikipedia , lookup
Genetic drift wikipedia , lookup
Genetics and the Origin of Species wikipedia , lookup
Schedule Change! Film and activity next Friday instead of Lab 8. (No need to print/read the lab before class.) Today: Thinking About Darwinian Evolution Part 1: Darwin’s Theory What is evolution?? And what is this finch doing?!? Perplexing Observations… We owe much of our understanding of EVOLUTION to CHARLES DARWIN. Darwin’s Origin of Species (1859): 1. Descent with Modification (Evolution) 2. Natural Selection as a mode of Evolution (Remember: Mendel publishes in 1866…) Darwin’s Natural Selection: Observation #1: Individual Variation Darwin illustrates his mechanism with examples from ARTIFICIAL SELECTION, the breeding of domesticated plants and animals Observation #2: Struggle for Existence Inference: Differential Reproductive Success or Natural Selection If artificial selection can change so much in a relatively short time, argues Darwin, then natural selection should be capable of considerable modifications. 1 Darwin also proposed that natural selection, over time, could produce new species from ancestral species. This was his explanation for the 14 unique species of finches he observed on the Galapagos Islands. The Historical Context From 1600’s +, Geologists begin mapping multiple distinct layers of rock with fossils in them. Lines of Evidence Naturalists begin to study Biogeography: the distribution of organisms Many are unique to isolated places! Lines of Evidence: Comparative Morphology Lines of Evidence: Comparative Embryology Who’s who??? 2 Thus Darwin’s views are supported by multiple, independent lines of evidence. Evolutionary patterns of Homology that match patterns in space (Biogeography) and time (the Fossil Record). Examples of Natural Selection? •Insecticide-Resistant Insects •Antibiotic-Resistant Bacteria •Drug-Resistance in HIV ADAPTATIONS are the result of natural selection. Three Important Constraints on Natural Selection: 1. Natural selection occurs only at the POPULATION LEVEL. (Population =a group of interbreeding individuals of the same species, sharing a common geographic area.) 2. Natural selection can only amplify or diminish HERITABLE VARIATION. 3. Natural selection is SITUATIONAL; an adaptation in one situation may be useless or even detrimental in another. Population: localized group of individuals belonging to the same species. •Every species distributed over range, but composed of multiple populations. •Populations may be more or less isolated. •The total aggregate of genes in a population at any one time is its GENE POOL (all alleles at all loci) MICROEVOLUTION • Generationto-generation change in a population’s frequencies of alleles What could cause the frequency of a particular allele to change?? 3 Four Primary Causes of Microevolution: 1. Mutation 2. Natural Selection 3. Gene Flow 4. Genetic Drift 1. Mutations: • A change in an organism’s DNA can change the gene pool of a population • Important as the original source of Genetic Variation! • Mutations can be lethal, neutral, or provide an advantage! 2. Natural Selection: can affect Types of Selection: Examples?? the frequency of traits in the POPULATION in three different ways: 1. Directional Selection- favors one extreme 2. Diversifying Selection- favors variants at both opposite extremes 3. Stabilizing Selection- selects against the extremes 3. Gene Flow: Populations may gain or lose alleles due to the migration of fertile individuals or gametes between populations. 4. Genetic Drift: a change in a population’s allele frequencies due to CHANCE. Genetic Drift is most effective in small populations! 4 Types of Genetic Drift… 1.The Bottleneck EffectDisasters randomly reduce the population size. The surviving population may not be representative of the original population’s gene pool. Special Types of Selection: Sexual Selection Types of Genetic Drift… 2. The Founder Effect- a few individuals from a larger population colonize an isolated new habitat. Genetic drift occurring in this new colony is known as the founder effect Some traits are advantageous simply because males or females prefer them Polydactyly -- extra fingers or sometimes toes -- is one symptom of Ellis-van Creveld syndrome. The syndrome is commonly found among the Old Order Amish of Pennsylvania, a population that experiences the founder effect. Special Types of Selection: Balanced Polymorphisms Strange Mating Rituals… Two or more alleles maintained in a population by balancing selection. Example: Sickle Cell Disease High incidence due to increased malarial resistance! 5 HIV and Evolution… Malaria and Sickle Cell Disease… A colorized SEM of HIV emerging from a white blood cell. HIV, the AIDS Virus How HIV reproduces inside a CD4 + T lymphocyte (T cell) HIV is a retrovirus. A retrovirus is an RNA virus that reproduces by means of a DNA molecule. It copies its RNA to DNA using reverse transcriptase Let’s Watch… Integrase Protease HIV and Evolution… A combination of drugs that act on different viral targets can be used to fight HIV. This is known as highly active antiretroviral therapy (HAART). 6 HIV Evolution in a Single Patient Following Up… T0 T2 T1 You Try: In-Class, Part 1 7