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Today’s Plan • Course logistics • Mendelian segregation ONLINE RESOURCES Course web page is live http://dbs.umt.edu/courses/biol223 “Online Learning Center” for Genetics text http://www.mhhe.com/brooker Instructions on first couple of pages Register your iClicker at iClicker.com iClickers • Get one, bring it to class, use it at least once. • Register. If you registered your iClicker for Biol221 or another class in Fall 2008, you do NOT need to re-register. Otherwise, you do. • Relax, use the clicker in class. • Participation counts -- 50 pts will reflect iClicker use throughout the semester. **If you are having issues getting registered etc., come see me or call the iClicker help line.** Course structure Discussion sections (1 hour/week) • NO MEETING THIS WEEK • Next week, go to your preferred (enrolled) section. • An opportunity to discuss lecture topics in more depth and go over homework assignments. • Participation counts -- a 5 pt. exercise will start each session. See your TA beforehand if you need to miss your usual section meeting. Section CRN Time Room TA 02 3 0 23 0 T 9 -1 0 NS 20 7 Lindy 03 3 0 23 1 T 1 1 -12 HS 4 1 1 Ellen 04 3 0 23 2 Th 9 -1 0 NS 20 7 Jon 05 3 0 23 3 W 1 1 -1 2 NS 30 7 Ellen 06 3 0 23 5 W 1 0 -1 1 HS 1 0 2 Lindy 07 3 0 23 6 W 1 1 -1 2 HS 1 0 2 Lindy 08 3 0 23 7 T 1 0 -11 LA 33 4 Lindy 09 3 0 23 8 T 1 0 -11 LA 20 1 Ellen 10 3 0 46 1 Th 10 -1 1 NS 20 7 Jon 11 3 0 46 2 Th 11 -1 2 HS 4 1 1 Jon 12 3 0 49 3 T 1 -2 LA 24 9 Ellen 13 3 0 49 4 Th 1 -2 ED 3 12 Jon For next week • Turn in your HW1 to your TA’s folder at Monday’s lecture • Go to your section (some rooms have changed, so check!) Course structure Weekly Homework Assignments • Worth 10 pts. each (11 total, drop lowest 2) • Handed out in lecture each Monday and posted online. • Due in lecture the following Monday or by special arrangement with your TA by noon. • Answers are posted at 12:00 noon on Mondays, so no late assignments will be accepted. Course structure Exams • 2 midterms (125 pts each) • Comprehensive final (200 pts) • Each exam will have a take-home component (a more extended homework, basically) as well as in-class portion • In-class exams will be partly multiple choice and partly short answer/problem solving Course Structure - Grading Midterms (250) In-class exams (2) Take-homes (2) 100 pts each 200 pts 25 pts each 50 pts Discussion sections (150) HWs (top 9 of 11) Participation 10 pts each 5 pts each Final Exam (200) In-class exam Take-home 90 pts 60 pts 175 pts 25 pts iClicker Participation 50 pts Total 650 pts For more details on policies etc., see syllabus handout or course page. Questions?? Today... Basic transmission genetics Why do we study Mendel? Mendel’s 1st law of segregation Using Punnett squares to predict genotypic and phenotypic ratios in progeny Why do we study Mendel? Science is a process, not a collection of information. We study Mendel in order to understand the process of science. Gregor Mendel (1822-1884) “Father” of Genetics Observation Children resemble their parents. Question Why? Transmission Genetics Since 8000 BC – Neolithic farmers select plants and animals with desirable traits— the highest-yielding grain, the sweetest fruit, or the fattest cow. Transmission Genetics 400 BC – Greek philosopher Hippocrates proposes that tiny particles from every part of the body of each parent became blended, producing an individual with the characteristics of both. 350 BC – Aristotle dismisses Hippocrates’ theory, noting that children do not always resemble parents. But Aristotle’s thinking about heredity still centers on a mixing of “fluids” from each parent. Blending inheritance Plutarch (75 BC): “Drunkards beget drunkards”. Frequency of alcoholism in adopted children: Non-alcoholic biological-parents 5% One alcoholic biological-parent 30% Children of non-alcoholics raised by alcoholic parents 5% Based solely on these data, the tendency to become an alcoholic is – (a) Entirely genetic (b) Entirely environmental. (c) Both genetic and environmental. Darwin’s model of (blending) inheritance • Gemmules from parts of the body were passed on to progeny through the bloodstream • Francis Galton experiment in 1871: Blood transfusions in rabbits did not alter the color (black, gray, or white) of progeny. • Not very satisfying… Mendel’s motivation was to discover the mechanisms of inheritance that were needed for Darwin’s theory of evolution by natural selection. Darwin’s near miss. . . 1866 letter to A. Wallace "My dear Wallace... I do not think you understand what I mean by the non-blending of certain varieties… I crossed the Painted Lady and Purple sweetpeas, which are very differently coloured varieties, and got, even out of the same pod, both varieties perfect but none intermediate. Something of this kind I should think must occur at least with your butterflies & the three forms of Lythrum; tho' these cases are in appearance so wonderful, I do not know that they are really more so than every female in the world producing distinct male and female offspring... Believe me, yours very sincerely Ch. Darwin" Gregor Mendel • Contemporary of Charles Darwin • Paper published 1865; unnoticed until 1900 – The Origin of Species (1859) • Major contributions – Particulate nature of inheritance – Three Principles (1) Dominance (2) Segregation (3) Independent assortment Why did Mendel succeed? He asked the right question. He used an appropriate scientific method. He chose the right organism. Right Question Whoever surveys the work in this field will come to the conviction that among the numerous experiments, not one has been carried out to an extent or in a manner that would make it possible to determine the number of different forms in which hybrid progeny appear, permit classification of these forms in each generation with certainty, and ascertain their numerical interrelationships. It requires a good deal of courage indeed to undertake such a far-reaching task; however, this seems to be the one correct way of finally reaching the solution to a question whose significance for the evolutionary history of organic forms must not be underestimated. Gregor Mendel (1865) Scientific Method Observation Hypothesis Experimental Design Quantitative analysis Hypothesis testing Scientific Method Observation Hypothesis Experimental Design Quantitative analysis Hypothesis testing Scientific Method Mendel’s garden at Brno monastery Mendel’s notes on Phaseolus (beans) The right organism - garden peas (Pisum) • Many seeds per cross => large sample sizes • Short-generation time • Easy to self-fertilize and cross-fertilize • Discrete traits The right organism - garden peas (Pisum) • Many seeds per cross => large sample sizes • Short-generation time • Easy to self-fertilize and cross-fertilize • Discrete traits Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. White Remove stamens from purple flower. Parental generation Stamens Transfer pollen from stamens of white flower to the stigma of a purple flower. Purple Cross-pollinated flower forms seeds. Plant seeds from pod. Firstgeneration plants The right organism - garden peas (Pisum) • Many seeds per cross => large sample sizes • Short-generation time • Easy to self-fertilize and cross-fertilize • Discrete traits TRAIT VARIANTS Purple White Axial Terminal Seed color Yellow Green Seed shape Round Wrinkled Pod shape Inflated Constricted Pod color Green Flower color Flower position Height Tall Yellow Dwarf Experimental approach 1. Generated ‘true-breeding’ lines for each trait => parental generation (P) 2. Crossed two different true-breeding lines => 1st generation progeny (F1 hybrids) 3. Self-fertilized an F1 hybrid => 2nd generation progeny (F2 hybrids) Height Tall Dwarf P plants x Tall Dwarf F1 seeds F1 plants Selffertilization F2 seeds F2 plants Conclusions P generation Cross-fertilization Tall “dominant”. Dwarf “recessive”. F1 generation 100% tall progeny (hybrids) Self-fertilization Recessive type still present, hasn’t been “blended” away. F2 generation 787 tall 277 dwarf PHENOTYPE GENOTYPE TT P generation tt Cross-fertilization F1 generation 100% Tt (tall) 100% tall progeny (hybrids) Self-fertilization 25% TT F2 generation 75% tall 25% dwarf 50% Tt (tall) 25% tt (dwarf) P plants TT x tt x Tall Dwarf F1 seeds All Tt F1 plants Selffertilization Tt x Tt F2 seeds F2 plants TT + 2 Tt + tt Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Female reproductive cells (F1) Punnett Square Male reproductive cells (F1) T T t t Female reproductive cells Male reproductive cells T t T TT Tt t Tt tt (TT + 2 Tt )+ tt = 3:1 ratio Mendel’s Principles 1. Dominance: In a heterozygote, one allele may conceal another. 2. Segregation: In a heterozygote, two different alleles segregate from each other with equal probability during the formation of gametes. TRAIT VARIANTS Purple White Axial Terminal Seed color Yellow Green Seed shape Round Wrinkled Pod shape Inflated Constricted Pod color Green Flower color Flower position Height Tall Yellow Dwarf Repeated tests of model P Cross F1 generation F2 generation Ratio Tall X dwarf stem All tall 787 tall, 277 dwarf 2.84:1 Round X wrinkled seeds All round 5,474 round, 1,850 wrinkled 2.96:1 Yellow X Green seeds All yellow 6,022 yellow, 2,001 green 3.01:1 Purple X white flowers All purple 705 purple, 224 white 3.15:1 Axial X terminal flowers All axial 651 axial, 207 terminal 3.14:1 Smooth X constricted pods All smooth 882 smooth, 229 constricted 2.95:1 Green X yellow pods All green 428 green, 152 yellow 2.82:1 In whippets, the “bully” trait is caused by a recessive allele (b) at a single locus. You cross a “bully” female with a heterozygous male. What proportion of the resulting offspring would you expect to be bullies? (a) None. (b) 25% (c) 50% (d) 75% (e) 100% Normal Bully Heterozygous male (Bb) Bully female (bb) B b b Bb bb b Bb bb (c) 50% bully (bb) Key Terms P = parental generation homozygous F1, F2, Fn generations heterozygous phenotype, trait dominant genotype recessive gene locus (plural: loci) allele Mendels’ reasoning in modern terms 1. Each parent carries 2 “factors” (alleles) for a trait 2. The two alleles can be identical or different (true-breeding parents have 2 identical alleles and are termed homozygous) 3. When 2 alleles are different (individual is heterozygous) , one may dominant (determines the trait) and the other recessive (hidden) 4. Alleles segregate equally (50:50) and gametes fuse at random => Mendel’s 1st law of segregation Friday: Independent Assortment Course structure Question/Answer Sessions • Begin NEXT week • Thursdays 6:00-7:30 pm HS411 • Not a review, but an extra opportunity for you to ask questions about the lectures, reading or homework problems • Also my office hours: 9-11 MWF in HS309A and by appt. Scientific Method Whoever surveys the work in this field will come to the conviction that among the numerous experiments, not one has been carried out to an extent or in a manner that would make it possible to determine the number of different forms in which hybrid progeny appear, permit classification of these forms in each generation with certainty, and ascertain their numerical interrelationships. It requires a good deal of courage indeed to undertake such a far-reaching task; however, this seems to be the one correct way of finally reaching the solution to a question whose significance for the evolutionary history of organic forms must not, be underestimated. Gregor Mendel (1865)