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This 10 page Class Notes was uploaded by Beatrice Deckow I on Monday September 28, 2015. The Class Notes belongs to BIOL 303 at George Mason University taught by Staff in Fall. Since its upload, it has received 12 views. For similar materials see /class/215109/biol-303-george-mason-university in Biology at George Mason University.
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Date Created: 09/28/15
Evolution Evolution is the foundation of biology It explains why animals and other organisms look the way they do how they are related and even why they do what they do Basically it can explain just about anything in biology So what is evolution The change in organisms over time Or more precisely a change in the genetic makeup of a population over time But we re not done for a while Note This definition says nothing about fossils mimicry adaption etc These are the results of evolution The de nition merely talks about genetics So let s delve into evolution in more detail Five parts I History 11 Mechanism III Evidence IV Genetics V Evolution in actionexamples I History Fig 222 p 453 amp several Figures not in book mostly pictures ofthe following folks Linnaeus First organized animals into some kind of cohesive structure Grouped similar animals into similar categories and established a hierarchy of groups where the higher up one goes the more diverse the animals in each group Father of taxonomy More on this tomorrow Lamarck First to propose evolution as a concept But his mechanism was weird If an animal uses a particular part of its body a lot then that part will develop more eg athletes Thus animal acquires certain characteristics These are then passed on to the offspring this idea is basically wrong But Lamarck had great foresight the idea of evolution was a breakthrough it explained the fossil record and opened up the possibility of a long period of time for things to happen eg animals to change Cuvier opponent of evolution but first to recognize that the age of fossils varies in dilTerent rock strata Assumed that these represented species that had died out in that location but were still alive elsewhere father of paleontology made many contributions to anatomy as derived from fossil material Hutton and Lyell Scottish geologists Hutton noted that rock formations landscapes etc can all be explained by processes going on today Formation of river valleys Grand Canyon probably the most spectacular example mountains etc Gradualism big changes can take place over long periods of time Lyell developed uniformitarianism as well as elaborated and polished Hutton s ideas Hutton was an awful writer and it took Lyell to translate his ideas into readable English Uniformitarianism Things happen today in the same way as they did years ago For example the action of wind water volcanoes was and is the same throughout history It is true that this is an assumption of evolution IMPORTANT implication The earth is much older than was thought up until then Summary up until now The age ofthe earth is very old Evolution as a concept had been considered though the mechanism didn t make sense Darwin See text for some more details of his life Darwin and the Beagle by Moorehead In brief Was born in 1809 Grew up with an intense interest in biology Entered Cambridge to become a member of the clergy most naturalists were clergy at the time Shipped out on a five year voyage aboard the Beagle in 1831 Fig 225 p 455 While traveling across South America particularly the Galapagos he started to notice similarities and differences in animals and plants Started to develop some of his ideas Published many papers on his return to England but even though he wrote up a large essay on evolution he did not publish this until much later In 1859 spurred by Wallace he nally publishes The Origin of Species Maj or breakthrough in biology Carefully argued with extensive notes examples etc What was different The mechanism There was nally a mechanism that could explain evolution natural selection More on this in a moment Lived for many more years publishing numerous more books including the rst treatise on human evolution Also an expert on worms will come up again later Died in 1882 and was buried in Westminster Abbey Two more people you should know Wallace another great naturalist that independently developed evolution through natural selection did most of his work in Southeast Asia Spurred Darwin to write up his essay for publication Mendel Darwin could not explain how characteristics were passed on from one generation to the next Only that they were Mendel showed how though his work was not rediscovered until much later Considered the Father of genetics With genetic understanding all the pieces of how evolution works were nally in place Darwin had a copy of Mendel s paper on his bookshelf similarly Mendel read the Origin of Species but neither put the pieces together II Mechanism of evolution Natural selection Darwin s and Wallace s great insight l Organisms vary In any group of animals organisms not all are the same look around room Incidentally most differences but not all are due to genetics 2 All organisms produce more offspring than can survive Roach display at Museum of Natural history Malthus rst to realize this attributed much misery to populations outstripping food supply populations can t keep growing inde nitely even today population growth is considered a major problem 3 Therefore only some offspring survive Which ones The ones best suited to their environment For example the quickest the ones with the best camou age or the least clumsy the most intelligent etc The number of organisms with this trait will then increase at the expense of others in other words the population can change particularly if the environment changes 4 The organisms with these genes will survive to pass on their genes to the next population Darwin didn39t know about genes this last bit comes from Mendel39s work 4 If the environment changes then the population will respond by changing with it or die Thus if a new predator is introduced population will hopefully become faster NOT by wanting to be faster but because faster individuals survive See page 458 in your text for a di erent breakdown it s the same thing but explained a little differently III Evidence of evolution Already mentioned antibiotic and insecticide resistance Evolution is an ongoing process and is happening right now both insecticide amp antibiotic resistance are major problems right now Fig not in book Fossil record probably the most obvious evidence Fossils are records of past life What kind most obvious bones or hard parts often preserved by being submerged in areas with low oxygen prevents slows rotting Compressed then bones are often replaced by minerals seeping in from the surrounding rock Literally turns tissues into rock Fig 223 p 453 under rare circumstances may preserve soft parts Mammoth obvious example Fig not in book As one examines fossil record one sees organisms changing as one moves from older rocks to newer rocks Fig 2525 p 530 Comparative anatomy Similar structures in living organisms As one looks at animals which are more closely related one sees structures that are more similar Well see several examples of this in lab both the taxonomy and evolution labs Gives rise to some more concepts Convergent evolution animals that are different evolve similar structures due to similar environmental pressures A classic example is the body shape of fish dolphins amp ichtyosaurs extinct These animals are unrelated yet have very similar body shapes Homologous structures structures that have a common origin but may be used for different things Fig similiar to 2217 p 463 Analogous structures structures that look similar but have di erent origins e g wings in birds and insects An example Wings in birds and bats are analogous BUT most of the bones that make up these wings are homologous If you understand this you have a decent grasp of the concepts involved the bones can be traced to a common ancestor the wings can not Fig not in book Embryology Embryos show common ancestry for example gill slits in human embryos Many embryos from totally di erent species look identical at various stages in their development Fig not in text but see g 2218 p 463 Biochemistry Mostly but not entirely DNA Similar species have DNA ie genes that are very similar This can be used to establish lineages and other relationships Used even in society to establish identity of criminals as well as parentage DNA fingerprinting is based on this idea etc For example children will have DNA more similar to their parents This works even on a larger scale such as between species Fig not in text proteins are based directly on DNA Biogeography Good schools offer courses in this This is one of the things Darwin noticed The further away he got from home the more different the species were from those he recognized In particular older animal groups often were more widespread The closer geographically related animals were the more likely they were to be similar The further apart two animals the more time they ve had to evolve in their own direction Additionally using fossil evidence and evidence from geology e g continental drift we can explain the distribution of organisms eg why llamas occur in South America and their closest living relatives camels live in Asia Arti cial selection Fig not in book and Fig 229 p 458 One of Darwin s more powerful arguments Humans have been breeding plants and animals for thousands of years Today many are completely di erent from ancestral species Dogs Cats Horses Wheat etc are all good examples Humans decide which organisms are allowed or encouraged to reproduce Other evidence Camou ageadaptation Fig 2212 p 459 Moths in northern England industrial pollution OVERHEAD 2 not in book dark moths started appearing with the onset of pollution in the 1850 s population studies have con rmed that birds are the selecting force recently with new environmental regulations the trend is being reversed Mimicry Details in lab Some animals have evolved to look like other animals Why Classic example One animal is toxic or venomous e g Coral Snake Other animals take advantage of this by looking or sounding like the dangerous one so they won t be bothered eg Scarlet King Snake See section on mimicry on page 1179 1180 in your text there are also a couple of illustrations on these pages IV Genetics a lot of the following was discovered by Mendel We won t go into the details here in Genetics class But in general we need to know the following Appearance is controlled by 1 Genes genetic makeup 2 Environment e g suntan Environmental factors suntan are not passed on to offspring Lamarck Genes are passed on to o spring What are genes gene basic unit of heredity which doesn t say much determines traits about an individual eye color hair color size even folding hands melanism in cats often a single gene or allele corn color ower color etc coat color in mice to gure out the specific trait we need to know about alleles di erent alternative forms of genes allele for brown or an allele for black coat color in mice A B 0 blood types in this case three alleles A B and 0 meaning neither A or B Sickle cell anemia question why do we have sickle cell anemia allele for normal allele for sickling So in general details in genetics if an individual or mouse has a black coat color it is likely some of his offspring will have a black coat Why not all offspring Most organisms we re familiar with have two copies diploid of everything In other words two copies of genes for blood type eg an allele for blood type A and an allele for blood type B or two copies of genes for coat color etc ONLY ONE ALLELE from each parent IS PASSED ON TO THE OFFSPRING in sexual reproduction Parents pass one allele for each trait to the offspring in an egg or sperm When sperm fertilizes the egg the fertilized egg now has two alleles for each trait So next question if an individual has two different alleles what does he look like Depends on how genes interact Most likely you have heard of dominantrecessive Coat color in mice Black is dominant brown recessive Brown is not visible it39s impossible to tell brown is there without DNA analysis unless black is absent BB black Bb black bb brown Other possibilities blood groups in human AA type A BB type B 00 type 0 AB type AB AO type A B0 type B in my notation 0 means neither A nor B Note that neither A or B are dominant over each other but both are dominant over 0 Suppose that a recessive allele is lethal all mice with brown coat colors die What happens to frequency of brown allele gt Evolution change in genetic makeup of population Tay Sachs a human disease often works in exactly the same way What about sickle cell anemia Neither is dominant SS no sickle cell S S sickle cell SS some sickling under stress Now note The only way one can be SS is if one gets one of each allele from each of his parents SS folks suffer from malaria S S folks suffer from sickle cell SS folks are less susceptible to both When you take genetics you will learn that it is impossible in a probability sense to always produce heterozygotes every generation Last bit for genetics HardyWeinberg see the text for some of this though it s a bit confusing Suppose there are just two alleles eg coat color in mice Let s assume that in mice we have the following BB black Bb black bb brown But let s just think about the alleles for a minute B black b brown Now let s call the proportion of black alleles p The proportion of brown alleles well call q Obviously pq l or 100 and p lq and q lp So the probability of being BB pA2 read p squared bb q02 why rule of multiplication or simply pxp Bb 2pq why there are two ways you can be heterozygous or remember the binomial expansion from algebra But now note that everybody is either BB Bb or bb Therefore BB Bb bb p02 2pq q02 1 So we can gure out how common alleles are in populations How Measure people on a trait If it is dominantrecessive then we know BB Bb and bb can t tell the difference between BB and Bb Thus If we know of recessives bb Square root bb q or ofb alleles p lq so we know p Now we can just plug everything in BB p02 Bb 2pq and we already know bb Specific example see page 475 in text PKU genetic disease in humans occurs once out of every 10000 births qAZ 00001 110000 00001 q sq1tq02 001 p1q100199 p02 9801 2pq 20199 0198 or aprx 02 gt 2 of human population is a carrier for PKU and that s about as bad as math gets in Bio303 HardyWeinberg equilibrium however implies that the genetic makeup of a population does not change Why is this useful 1 This is sort of backwards but it shows under what conditions the genetic makeup of a population DOES change 2 Allows us to take a snapshot of a population and gure out genetic makeup as above Rules for a population to stay in HardyWeinberg equilibrium see p 474 1 Large population size no random effects from really small populations Fig 238 p 476 2 No movement of genes in or out of population 3 No net mutations we haven t really talked about mutations 4 Random mating 5 No natural selection Obviously very few of these hold over time give some examples But principle is useful for getting snapshots particularly with organisms having large generation times In lab we will see what happens when 5 is violated Finally a word about mutations details in Genetics Where do new alleles come from gt Mutations Most are harmful many are irrelevant a few are beneficial ie increased speed etc Causes environment Damage to DNA again details in genetics Original source of variability in populations provides raw material for evolution Mutations are the driving force behind evolution and the ultimate source for variability which natural selection can work on
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