Week 2 Notes!
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This 8 page Class Notes was uploaded by Arielle Menn on Sunday October 11, 2015. The Class Notes belongs to Biol 180 at University of Washington taught by Scott Rider Freeman in Summer 2015. Since its upload, it has received 25 views. For similar materials see Introductory Biology in Biology at University of Washington.
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Date Created: 10/11/15
Monday Oct 5th Natural Selection Conted Monday ctober 5 Z 15 1233 PM This lecture was given by Prof Dooley Housekeeping O A message from the Field Trip coordinator Field trips open tonight at 8 Login info is the same as for clickers There are gt90 trips to 17 different locations Trips range from 3 hours to overnight Mostly on weekends 1 field trip is required you can sign up for 1 max Field trips don39t excuse you from lab You can get 25 points equivalent to 14 of 1 exam However you can lose 10 points for missing your trip cancelling lt24 hours beforehand or showing up unprepared the trip coordinator will email you details before the trip OOOOOOO Goals for This Class conted from Wed 93015 0 Become a critical thinker 0 Learn professionalism amp integrity DON39T CHEAT ON CLICKER Q39s Evolution by Natural Selection conted from Fri 10215 0 We introduced Lamarckian evolution and evolution by special creation on Friday 0 Think about where do species come from and how have they come to be so well adapted to their environments 0 Think about the evidence amp the experiments 0 Frame answers in terms of 1 what are the species 2 how did they originate and 3 where did we get variation 0 What39s the key difference between Lamarckian evolution and Natural Selection Lamarckian evolution is progressive whereas natural selection is random responsive but doesn39t strive to change the species in any particular direction 0 What are the four postulates of Natural Selection 1 Individuals within populations are variable 2 Some of these variations are passed on to offspring 3 Not all individuals produce the same number of offspring 4 Individuals with certain heritable traits produce most offspring 0 To summarize Heritable variation leads to differential reproductive success 0 Key Point Evolution is a result of the differential reproductive success 0 Individuals do not evolve evolution only happens on the level of an entire population Biology 180 Page 1 Tuesday Oct 6 Mendel amp Monohybrid Crosses Tuesday ctober 6 2 15 126 PM This lecture was given by Prof Dooley Housekeeping 0 Office hours start next week Natural Selection conted from Mon 10515 0 Yesterday we condensed Darwin39s Theory of Evolution to the two points 1 Heritable variation 2 Leads to differential reproductive success 0 We discussed that 0 Individuals don39t evolve and pass on traits they39ve gained throughout their lifetime to their offspring o The population as a whole evolves over time because of the selection for more survivable traits throughout the population 0 Evolution does act on individuals because they experience differential reproductive success they die or live they have more or fewer offspring etc 0 We also discussed some terms and how their biological definitions differ from their everyday 0 Theory a hypothesis that applies to a larger field a collection of hypotheses that relate to each other to explain a larger system 0 Fitness an individual39s ability to survive and reproduce as efficiently and effectively as possible 0 Adaptation a species39 change over time in response to environmental factors this adaptation is a gradual process resulting from the death or decreased fertility of those less adapted to surviving in the environment 0 Darwin was confused because even after evolution was accepted in the 18805 natural selection wasn39t really supported until the 192039s3039s o It seemed that genetic variation and sexual selection should over time homogenize entire populations into uniform creatures but that wasn39t being observed in the real world 0 The theory of blending inheritance also posed the question of why populations weren39t converging toward a median phenotype and becoming more uniformaverage over time Mendelian Genetics 0 Mendel introduced an answer to these questions with his green peas experiments 0 Mendel was a monk who was educated in the medicinebiology of the times after a serious illness 0 He decided to look into genetics by experimenting with pea plants as a model organism 0 Wait what39s a model organism o A relatively simple organism cheap easy to work with en masse preferably with a short generation time and quick turnover specifically for genetic studies and with easily observabletrackable phenotypes across generations 0 Whatever we study in model organisms should be applicable as directly as possible to other organisms so that findings can be extended as far across the biological spectrum as possible 0 So Mendel picked pea plants a great model organism 0 There were two existent pure lines of plants that displayed distinct phenotypes in seven different categories leaf shape seed smoothness etc 0 He tested all seven of the traits to make sure his results were consistent across a variety of traits as opposed to just one unusual trait 0 Side note Replicating an experiment requires keeping all the variables the same and doing the exact same experiment It is important both to replicate experiments to make sure original results weren39t a fluke and to do similar experiments with a variety of controlled settings and characters to supportrefute the hypothesis 0 What did Mendel find 0 Mendel crossed a pure line of tall plants with a pure line of dwarf plants then allowed the first generation of offspring F1 to selfpollinate and produce the second generation F2 0 He found that 100 of the F1 plants were tall but 75 of the F2 plants where tall while the other 25 were dwarf Biology 180 Page 1 o This refuted blending inheritance because the plants weren39t all middle height 0 So two new definitions 0 Gene a factor that influences for our purposes so far a phenotype of a particular trait and is passed on to offspring o Allele a version of a gene 0 Now we can claim 0 Inheritance is particulate blending doesn39t occur When we crossed two parents with different phenotypes we didn39t get a hybrid phenotype Each individual pea plant has two alleles of each gene Because traits that disappeared in F1 reappeared in F2 so an extra copy of that recessive allele must have been saved somewhere Individuals can be homozygous both alleles are the same or heterozygous the two alleles are different Some alleles are dominant to others others are recessive I Note Dominance and recessiveness are defined ONLY in terms of the appearance of heterozygotes I Note most alleles are neither dominant nor recessive During gamete formation in a parent pairs of alleles segregate separate and go into different gametes I Each gamete contains one allele of each gene Male and female gametes fuse during fertilization to form a zygote I Each offspring then has two alleles one from each parent 0 O O O 0 Biology 180 Page 2 Wednesday Oct 7th Punnett Squares amp Mendelian Gene cs Wednesday ctober 7 2 15 129 PM This lecture was given by Prof Dooley Housekeeping O We39ll be getting an email with a test about our baseline level understanding of bio concepts and we can allow our results to be released into a research study 0 Our prof won39t know whether we release our data to the study until after the quarter and will have no bearing on our grade Punnett Squares 0 Today39s Question How are alleles from diff genes transmitted to offspring together or independently 0 We analyzed the inheritance from one trait monohybrid cross 0 Now let39s look at two traits at once dihybrid cross 0 Do the two traits stick together and sort dependently 0 Or do they act completely separately independent assortment 0 Let39s draw a Punnett Square for dependent assortment 0 Say you have a tall purple homogenous parent PP39I39I39 and a short white homogenous plant pptt o All of the offspring would be heterozygous in both traits genotypically o All of the offspring would display the tall purple phenotype 0 When allowed to selfpollinate the heterozygous F1 will produce 0 The genotypic ratio will be 121 o The phenotypic ratio will be 31 0 14 of the F2 will be short white flowers 0 There will be no tall white plants or short purple plants 0 Now let39s look at a Punnett Square for Independent Assortment W V F 0 The top and side represent the Vk l four possible trait rt 3 rt V a PT 479W combinations that could be in found in the gametes of our 17 Wt 100 heterozygous F1 plants 0 The phenotype ratio is 9331 to l PPTT Pp 0 Tall white plants and short purple plants exist gp rt 9 We l7rt fr rrquotC 0 Side note Ratios deal with whole numbers frequencies have decimalsfractions because they need to add up to 1 and deal with actual data from a limited sample size as opposed to the ideal ratio from an unlimited population 0 Mendel concluded from the actual data he found with his pea plants that independent assortment was what39s actually happening in genetics 0 Note this is kinda misleading More in lab and later in the course 0 To understand the physical basis of Mendel39s rules how genetic variation works we need to look at two types of cell division that were first described in the late 18005 O Mitosis The process responsible for asexual reproduction and growth in multicellular organisms O Meiosis Sexual reproduction reduced lpxg 1 Biology 180 Page 1 O Mitosis How does it work 1 2 3 4 5 Prophase DNA is replicated into two sister chromatids from each chromosome Metaphase chromosomes line up along the middle of the cell metaphase plate Anaphase sister chromatids separate and travel toward opposite ends of the cell Telophase cell starts to pinch in towards the middle resembling more of a peanut shape than a bubble Cytokinesis the cell separates into two separate but identical cells 0 Notation Haploid Number vs Ploidy 0 We use n to indicate the number of diff types of chromosomes found in a species this is known as the haploid number We use a numeral before n to indicate the number of each type present this numeral represents ploidy ex Humans are diploid because we produce two copies of each chromosome horses are triploid A chromosome is an unreplicated collection of DNA represented as a strand A chromatid is a replicationcopy of a chromosome that is created during mitosismeiosis to help create multiple identical copies of the same DNA A chromosome that is replicated looks like two chromatids side by side still counts as one chromosome Biology 180 Page 2 Thursday Oct 8th Mendelian Genetics Thursday ctober 8 2 15 127 PM This lecture was given by Professor Freeman Housekeeping 0 Study habits 0 DON39T spend all your time rereading the textbooktaking notes on readings 0 Practice in study groups quiz each other constantly 0 Use the blue questions in the readings in the textbooks to double check your knowledge 0 Only reread the textbook for specific sections once you39ve diagnosed what you don39t understand Meiosis vs Mitosis Review Ha walk 3 ltgt Meiosis 1 is a ploidy reduction PkgHM 3L b Each chromosome replicates but the ploidy number stays the 5 same b Homologs synapse which means sister chromosomes find each other so it looks like four copies bound in a bundle because there d are two chromatids corresponding to each of the two sister chromosomes at least in a diploid cell b Crossing over occurs so the copies of the sister chromosomes exchange information in this little bundle of four chromatids gt Then the sister chromosomes separate and travel to opposite ends of the cell so even though you see two strings going to each side Q 5 3 of the cell those two strings represent the two chromatids for 397 HotV39O0 only ONE chromosome Therefore at this phase the cells go from 70390395 N s diploid to haploid with each individual chromosome still in its aw arrow Lt waved grade replicated chromatld state 39J 0quot ltgt Meiosis 2 is stays in a haploid state b You have one of each chromosome sitting in a haploid daughter cell in a replicated state so it looks like two identical chromatids b The chromatids line up on the metaphase plate down the middle of the cell and separate again b Each daughter cell how has only one chromatidreplica of one chromosome it39s still haploid b At this point there are ready gametes and the cell will only become diploid again after fertilization when it joins with another person39s haploid gamete Mendelian Genetics conted from Wed 10715 0 The Chromosome Theory of Inheritance 0 Pattern Component Mendel39s Rules 0 Process Component Meiosis O Inheritance patterns exist the way they do because genes are gathered on chromosomes 0 Proposition 1 The principle of segregation results from the separation of homologous chromosomes Q a Q 0 During Meiosis I the following happens 9 A 0 Biology 180 Page 1 Q l 0 During Meiosis I the following happens V thWY IW l3 0 Then they segregate Notice this act of segregation illustrates Mendel39s results from the pea plant experiments 0 Proposition 2 The principle of independent assortment happens because maternal and paternal chromosomes line up independently at metaphase of meiosis I That is in two traits that live on two different chromosomes those sets of chromosomes will synapse independently and segregate independently as well Biology 180 Page 2 0 What predictions does the chromosome theory make 0 Side note for right now our definition of mutation is a genetic change that prompts a phenotypic change 0 Drosophila experiments 0 White eye was the first phenotypic mutation found found in a male I Crossed to red eye wild type females all F1 were male I F2 phenotypes were 31 redwhite BUT all white eyes were male 0 But then in another cross some of the F2 females have white eyes 0 Meanwhile a woman named Nettie Stevens had discovered sex chromosomes in grasshoppers Biology 180 Page 3
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