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Evidence of Evolution 1. Fossil Record 2. Geographic Distribution of Living Species 3. Anatomical similarities - homologous Body structures 4. Similarities in Embryology 5. The more closely related, the more similarities in DNA. January 19/20, 2012 • Quiz • Mechanics of Evolution lecture • Natural Selection Lab • Be sure other labs are ready to turn in. Mechanisms of EVOLUTION VOCABULARY REVIEW • EVOLUTION – CHANGE OVER TIME • NATURAL SELECTION - INDIVIDUALS BETTER ADAPTED TO THE ENVIRONMENT ARE ABLE TO SURVIVE & REPRODUCE. – A.K.A. “SURVIVAL OF THE FITTEST” NEW VOCABULARY • POPULATION – GROUP OF INDIVIDUALS OF SAME SPECIES THAT INTERBREED • GENE POOL – COMMON GROUP OF ALL GENES PRESENT IN A POPULATION Variation in Populations 2 processes can lead to this: Mutations change in DNA sequence Gene Shuffling – from sexual reproduction Gene Pool Combined genetic info. of all members Allele frequency is # of times alleles occur Genetic Drift changes populations……. • Random change in allele frequency causes an allele to become common • Founder Effect: a cause of genetic drift attributable to colonization by a limited number of individuals from a parent population • Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations) • Nonrandom mating aka artificial selection: inbreeding and assortive mating (both shift frequencies of different genotypes) Evolution of Populations Occurs when there is a change in relative frequency of alleles………. in other words – a change in the contents of the gene pool • Natural Selection: differential success in reproduction; only form of microevolution that adapts a population to its environment Sexual selection • Sexual dimorphism: secondary sex characteristic distinction • Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism Phenotype Expression • Depends on how many genes control that trait Single-Gene vs. Polygenic Traits Single-Gene: 2 Distinct Phenotypes (EG: tongue rolling) Polygenic: Many Phenotypes Natural Selection on Polygenic Traits • Shifts to middle range • Shifts to 2 extremes • Shifts to 1 extreme Allele Frequencies Natural Selection Single Gene Traits Genetic Drift Polygenic Traits Directional Selection Stabilizing Selection Disruptive Selection SPECIATION THE FORMATION OF NEW SPECIES • AS POPULATIONS ARE ISOLATED , THEY BECOME REPRODUCTIVELY ISOLATED • REPRODUCTIVE ISOLATION – MEMBERS OF 2 POPULATIONS CANNOT INTERBREED & PRODUCE FERTILE OFFSPRING. • REPRODUCTIVE ISOLATION LEADS TO SPECIATION 3 ISOLATING MECHANISMS…….. • BEHAVIORAL ISOLATION- CAPABLE OF BREEDING BUT HAVE DIFFERENCES IN COURTSHIP RITUALS (EX. MEADOWLARKS) • GEOGRAPHICAL ISOLATION – SEPARATED BY GEOGRAPHIC BARRIERS LIKE RIVERS, MOUNTAINS, OR BODIES OF WATER (EX. SQUIRREL) • TEMPORAL ISOLATION – 2 OR MORE SPECIES REPRODUCE AT DIFFERENT TIMES. Table 23.1a Fig. 23.6 Four species of leopard frogs: differ in their mating calls. Hybrids are inviable. These squirrels live on opposite sides of the Grand Canyon. This is an example of allopatric speciation. Hawaiian Honeycreepers An example of adaptive radiation – these species all diverged from a common ancestor (founder species) FOUNDER SPECIES SPECIATION IN DARWIN’S FINCHES • SPECIAITON IN THE GALAPAGOS FINCHES OCCURRED BY: - FOUNDING OF A NEW POPULATION, - GEOGRAPHIC ISOLATION which led to - REPRODUCTIVE ISOLATION and CHANGES IN THE NEW POPULATION’S GENE POOL due to COMPETITION. Table 23.1b Tigon Result of male tiger and female lion mating incaptivity. Offspring are infertile. Separated both geographically and ecologically. Liger Result of male lion and female tiger mating in captivity. Offspring may be infertile. http://www.youtube.com/watch?v=7dx2CUMtZ-0&feature=related http://www.youtube.com/watch?v=OmLgbY8gBN8 http://www.youtube.com/watch?v=UpoGfbQ0l8o&feature=related http://www.youtube.com/watch?v=eI_quJRRGxk&feature=related Conditions needed for Genetic Equilibrium