1 BIO 1120 Week 13 11 17 15 Evolution in Action Evidence of evolution within the fossil record fossil record provides evidence of organisms appearing and going extinct transitional forms fossils that indicate an organism that is part of a transition over millions of years from one species to another whales started as land dwellers whales now are entirely aquatic with no hind limbs basilosaurus was a transitional form entirely aquatic but with reduced hind limbs Comparative anatomy comparison of body structures of organisms can reveal remodeling of structures inherited from ancestors Bioinformatics use of computers to analyze sequence data from DNA and proteins reveals that closely related species have more similar DNA and proteins than more distantly related species 2 Populations are the units of evolution when Darwin published The Origin scientists did not yet understand DNA Darwin knew traits were often passed down but not specifically how that By the mid 1900s scientist had begun to put Darwin s work together with one of the most common misconceptions about evolution is that individuals genes or heredity occurred genetics evolve natural selection does work on the individual an individual lives or dies has offspring or not evolution is a change in the gene pool of a population over time over group of individuals of the same species living in the same place at the same generations Populations time Gene pools all the alleles of a gene in a population at one time every member of a population has a unique set of traits 3 mutations add alleles to a gene pool sexual reproduction creates unique combinations evolution is a change in allele frequency in a gene pool Micro Evolutions evolution an a small scale population changes slightly over time more brown rabbits less gray rabbits Evolution proceeds through several mechanisms genetic variation mutations random errors in the DNA can be good bad or nothing at all sexual recombination during formation of eggs and sperms Darwinian fitness what is fit next generation fitness is measured in terms of how many offspring you contribute to the an organism might not have to be fast or sting if it hides well 4 mechanism for evolution 4 gene flow genetic drift bottleneck founder effect natural selection sexual selection mutation adds new alleles to a gene pool Gene flow individuals migrate into or out of a population allows for exchange of alleles in planets drifting pollen carries alleles to distant trees Genetic drift change in a gene pool due to random chance in a large population death of a few individuals has little impact in small population death of a few individuals removes genetic diversity Bottleneck effect type of genetic drift Founder effect type of genetic drift a population is drastically reduced and recovers the new population often has greatly reduced genetic diversity a small group leaves a population to found a new population 5 NO gene flow with original population new population often has reduced genetic diversity Sexual selection form of natural selection where certain individuals are more likely to attract mates and thus have more offspring males may be more likely to die in combat but that is offset by being more attractive to females Macroevolution encompasses large scale changes microevolution was about small scale changes macroevolution is about the appearance or disappearance of species Species are maintained by reproductive barriers species population that is capable of interbreeding and producing healthy fertile young bacteria reproduce asexually fossils can t tell if they interbred or were fertile Behavioral isolation calls members of a species identify each other through coloration behaviors and 6 Mating time differences many species only reproduce at specific times of the year a spring species will not be fertile when a summer species is ready and vice versa Habitat isolation if species live in different habitats they may never meet Mechanical incompatibility anatomical differences prevent mating or fertilization Gametic incompatibility Hybrid weakness sperm from one species cannot fertilize an egg from another species if two members of different species do mate and produce an offspring that offspring will not be fertile sterile offspring cannot have its own offspring Speciation can occur through various mechanisms pace of speciation varies graduated model small changes over time punctual model 7 fast change followed by periods of no change 2 mechanisms for speciation allopatric speciation allo means other a species is separated into two populations by some physical barrier for such a length of time that if the 2 groups are brought back together they can t make fertile offspring sympatric speciation sym means same something happens in a population that makes some members incapable of reproducing with the rest of the population