Biol Week 5 Notes
Biol Week 5 Notes Biol 180
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This 8 page Class Notes was uploaded by Nikki Hovland on Wednesday October 28, 2015. The Class Notes belongs to Biol 180 at University of Washington taught by Scott Freeman in Summer 2015. Since its upload, it has received 76 views. For similar materials see Introductory Biology in Biology at University of Washington.
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Date Created: 10/28/15
INTRODUCTORY BIOLOGY 180 Thursday October 29 2015 Week 5 Notes Lecture 16 Misconceptions about Natural Selection KEY individuals do not change only populations do during natural selection process individuals don t change their genotypestraits gt a specific trait may become more prominentfrequent in a population over time because the individuals with the advantageous trait survived and produced more offspring a consistent environment favors long lifespan and slow reproduction natural selection is not same as Lamarck s inheritance individuals cannot pass on traits that changed during their life to meet environmental needs they are not heritable evolution occurs in populations NOT individuals like Lamarck claims natural selection is a SORTER it does not change existing variations in characteristics only acts on preexisting traits natural selection has design constraints can t have all of the best traits a compromise acclimatization is NOT adaptation changes in phenotype in response to environmental change acclimatizing are not passed on to offspring because no alleles have changed acclimation does not cause evolution evolution is not oriented towards a particular goal mutations just happen they don t happen for a purpose or to solve problems adaptations don t occur because an organism wants the trait or needs it contrary to Lamarck evolution is not progressive and does not always get better or more progressive most complex traits can be lost or made simpler vis natural selection no chain of greater beings one species is not superiorhigherbetter than another just different INTRODUCTORY BIOLOGY 180 Thursday October 29 2015 however evolution is not entirely random natural selection is not random BUT mutations are random AND random changes in allele frequencies like drift and gene flow are random 39 organisms often do not act for the good of the population and sacrifice themselves selfishcheater alleles are those that allow an individual to survive and reproduce a selfish behavior in contrast with a selfsacrificing allele that would cause the individual to die and not produce offspring thus not passing on its alleles constraints on natural selection nonadaptive traits like vestigial structures not adaptive they exist because of common ancestor genetic constraint of genetic correlation when natural selection cannot optimize a particular trait because of pleiotropy one allele affects many traits lack of genetic variation natural selection can only sort what is already present in the genes it can t create genes to produce a particular trait that may be better for fitness if genes are not already in individual s genome fitness tradeoff compromise between traits regarding how they affect the individual in the environment selection acts on several traits at once so basically every adaptation is a compromise all traits have evolved from previous traits Lecture 17 Mutation and Genetic Drift NOTE slide 1 clicker question on lecture notes is VERY IMPORTANT key important concept in biology evolution by natural selection adaptations do not ENSURE survival of population no NEED natural selection is NOT RANDOM natural selection acts on INDIVIDUALS not species INTRODUCTORY BIOLOGY 180 Thursday October 29 2015 genetic drift change in allele frequency in a population due to chance occurs randomly and sampling error occurs change of allele frequencies due to luck alone the frequencies of the sample of the population is much different than the whole population occurs in every population most prominent in SMALL POPULATIONS genetic drift is random in terms of fitness not adaptive genetic drift can lead to loss or fixation of alleles over time genetic variation loss when either of these happen generation after generation genetic marker specific allele that causes certain phenotype null hypothesis for hypothesis of genetic drift allele frequencies do not change and are instead in Hardy Weinberg proportions this DECREASES genetic variation WITHIN populations but INCREASES genetic differences BETWEEN populations 2 types of genetic drift How drift can be caused founder effect change in allele frequencies when a new population is created ie individuals immigrate to new area particularly prominent in small populations think of Pilgrims they were the FOUNDERS of our nation they came from Britain to America to create a new population bottleneck effect sudden reduction in number of alleles present in a population causing change in allele frequencies often occurs with natural disasters and disease wiping out huge portion of population randomly also prominent in small populations especially mutation one of the key methods of evolution that increases genetic variation since most natural selection genetic drift and possibly gene flow reduce it 3 types point mutation random single change in nucleotides in DNA INTRODUCTORY BIOLOGY 180 Thursday October 29 2015 chromosome level can duplicate genes and either cause genes to lose function or create new alleles ateral gene transfer can increase genetic variation as one species passes genes to another species example plasmids in bacteria mutation just happens RANDOM in regards to FITNESS beneficial allele allows individual to produce more offspring mutation is a SLOW EVOLUTIONARY PROCESS compared to selection gene flow genetic drift does not cause a lot of change on its own BUT can have a major effect when it occurs along with one of the other evolutionary processes KEY mutation is ultimate source of genetic variation only process that creates NEW ALLELES and without it evolution would eventually stop mutation alone usually doesn39t change allele frequencies Lecture 18 Gene Flow and Inbreeding gene flow individual leaves one population and JOINS a new population bringing in new alleles to population organisms emigrate from original population and immigrate to new population gene flow is TECHNICALLY the movement of alleles from one population to another different from genetic drift founder effect because individual leaves population and joins new one in gene flow but in founder effect a small portion of a population breaks off and forms a new population usually one outcome of gene flow allele frequencies become equal between original population and new population receiving the alleles gene flow is RANDOM regarding FITNESS can increase or decrease fitness INTRODUCTORY BIOLOGY 180 Thursday October 29 2015 reduces genetic variation BETWEEN populations allele frequencies become more alike over time inbreeding form of nonrandom mating where relatives mate or like selfing in plants increases homozygotes in population takes alleles from heterozygotes and makes homozygotes homozygotes inbreeding gt more homozygotes heterozygotes inbreeding gt homozygotes and heterozygotes in 121 ratio only half are heterozygotes inbreeding does not cause evolution no change in allele frequencies in pop only genotype frequencies not evolutionary process BUT can speed up evolutionary change because it can increase how fast natural selection eliminates recessive deleterious alleles from a population because they don t hide out as much as in a noninbreeding population decreasing heterozygotes can be detrimental to population because there are many cases where heterozygotes have an advantage in case of fighting disease and decreases fitness 39nbreeding depression decline in population fitness when homozygosity increases and heterozygosity decreases KEY inbred offspring expected to have LOWER FITNESS than outcrossed offspring SUMMARY 39 natural selection certain alleles favored maintainreduceincrease variation increase fitness gene flow aee move from one population to another makes two populations more alike INTRODUCTORY BIOLOGY 180 Thursday October 29 2015 tends to decrease variation in original population removes alleles increase in new population adds alleles random fitness 39 genetic drift random changes in allele frequencies founder effectbottleneck effect decreases variation random fitness mutation creating new alleles increases variation random fitness Lecture 19 Phylogenies and Tree of Life species evolutionarily independent population or group of populations 3 common criteria to identify species biological species concept identify species based on reproductive isolation no gene flow between pop that don t reproduce with each other pre zygotic isolation prevents individuals from diff species from mating Dost zvgotic isolation offspring do not survivereproduce when two individuals from different species mate PROBLEM cannot evaluate in fossilsasexual reproducers or when closely related species live far away morphospecies concept lineages differ by size shape or other morphological features useful for when have no data about gene flow and applies to sexual asexualfossil species INTRODUCTORY BIOLOGY 180 Thursday October 29 2015 PROBLEM subjective may lead to naming a single species as more than one species and can t separate species that differ by other things other than features phylogenetic species concept identify based on history of evolution of populations Darwin s theory of common ancestry monoohvletic groupcladelineage an ancestral population all descendants and only those one one phylogenetic treegt many monophyletic groups synapomorphy trait found in certain groups and common ancestor but not found in distant ancestors homologous traits can apply to any population and logical bc based on synapomorphies species is the smallest monophyletic group on tree of life under this concept PROBLEM only covers small number of populationsnot many currently available key we use a combo of these three concepts to identify species phylogenetic tree summary of history of ancestordescendant relationships branches represent population through time out group is a species closely related to the group being studied root is the furthest ancestor polygamy is a node that shows three or more descendants tip represents living or extinct group of genesspeciesphylaother taxa cladistic method relationships between species can be reconstructed based on the identification of shared derived characters called synapomorphies homoplasy same form similarity in organisms due to other reasons than having a common ancestor convergent evolution natural selection favors similar traits in different species as a result of similar ways of living leads to homoplasy INTRODUCTORY BIOLOGY 180 Thursday October 29 2015 polyphyletic group is a group that is not including the most recent common ancestor paraphyletic group is a group that includes common ancestor but not all of descendants 39 tree that shows the fewest evolutionary changes is usually the one that is the most accurate because independent evolution of traits is rare compared to similarity due to common descent