BIOL 1108 1st Edition Exam 1 Study Guide Lectures 3 12 Lecture 3 August 16 I Concept 22 3 Evolution is supported by an overwhelming amount of scientific evidence and there are four processes by which evolution occurs direct observation of evolution homology the fossil record and biogeography Direct observations of Evolutionary change Natural selection in response to introduced plant species Many animals have created adaptations in order to feed on different plants For example the soapberry bug in south Florida feeds on the native plant the balloon vine The soapberry bug eats the seed inside the vine by using its beak However in central Florida the soapberry bugs feed on goldenrain trees The bugs feed most efficiently when their beak is the same depth as the seed in the fruit On average the soapberry bug that lives in south Florida has a higher beak length than that of the central Florida bug This is because the balloon vine seeds are deeper than that of the goldenrain trees From the results we can conclude that a change in size of the soapberry bug s food source can result in evolution by natural selection for matching beak size The evolution of Drug Resistant Pathogens In 1959 scientist developed methicillin a powerful antibiotic Within two years methicillin resistant strains appeared This happened because some bacteria were able to synthesize their cell walls without methicillin affecting it These individuals reproduced and passed on the resistant genes allowing more resistant pathogens to be created Natural selection is not a creative mechanism it is a process of editing Natural selection depends on time and place It favors those characteristics in a genetically variable environment Homology Homology similarity resulting from common ancestry Many animals that have common ancestors result in having similar structures which are called homologous structures Homologous structures represent variations on a structural theme that was present in their common ancestor Example human arm cat leg whale fin and bats wing Vestigial structures are remnants of features that served a function in the organism s ancestors Example post anal tail and pharyngeal pouches in both a chicken and human embryo Homologous characteristics form a nested pattern all life shares the deepest layer and each successive smaller group adds its own homologies to those it shares with larger groups Evolutionary tree a diagram that reflects evolutionary relationships among groups of organisms Convergent evolution the independent evolution of similar features in different lineages Example flying squirrel and sugar gliders ability to glide Analogous share similar function but not common ancestry Fossil Records Fossil record documents the pattern of evolution showing how past individuals differed from present day organisms They also show evolutionary changes that have occurred in various groups Example the pelvic bone in fossil stickle back fish reduced in size over time in different lakes Biogeography II Biogeography the geographic distribution of species Influenced by factors like the continental drift Pangea The united all Earth s masses in one large continent 250 million years ago Endemic species of plants of animals that are not found anywhere else in the world Concept 23 1 23 4 24 1 Microevolution the change in allele frequencies in a population over generations Genetic variations difference among individuals in the composition of their genes or other DNA segments In genetic variation the phenotype does not matter Without genetic variation evolution cannot occur Characters that vary within a population may be discrete or quantitive Discrete characteristics can be classified on an either or basis they are determined by a single gene locus with different alleles that produce distinct phenotypes Quantitative characters vary along a continuum within a population usually result from the influence of two or more genes on a single phenotypic character Average heterozygosity the average percent of loci that are heterozygous To measure nucleotide variability biologist compare the DNA sequences of two individuals in a population and then average the data from many such comparison The nucleotide differences that provide the basis of genetic variation arise by mutation and other processes that produce new alleles and new genes New genetic variants are produced rapidly in organisms with short generation times In sexually reproducing organisms most of the genetic differences among individuals result from crossing over the independent assortment of chromosomes and fertilization Geographic variation differences in the geographic composition of separate populations Cline a graded change in a character along a geographic axis Population a group of individuals of the same species that live in the same area and interbreed producing fertile offspring Some populations can be geographically isolated from others but most are not A population s genetic makeup is describes by its gene pool which consists of copies of every type of allele at every locus in all members of population Every allele has a frequency in the population Hardy Weinberg principle states that frequencies of alleles and genotypes in a population will remain constant from generation to generation provided that only Mendelian segregation and recombination of alleles are at work EQUATION 2 2 p 2 pq q 1 Changes occur in genotype frequencies when atleast one of the conditions of the Hardy Weinberg equilibrium is not met 1 NO mutation 2 Random mating 3 No natural selection 4 Extremely large population size 5 No gene flow In Natural selection the phenotype matters Individuals in a population exhibit variations in their heritable traits and those traits that are better suited to their environment tend to reproduce more offspring than those whose traits are not suited for the environment It can cause adaptive evolution evolution that results in a better match between organisms and their environment In genetic drift chance fluctuations in allele frequencies over generations tend to reduce genetic variation Two examples are the founder effect and the bottleneck effect When a few individuals from a group become isolated the smaller group may establish a new population whose gene pool is different from the source group this is called the founder effect A severe drop in population size can cause the bottleneck effect This may happen from a sudden change in the environment Alleles