BIO 305 1st Edition Lecture 2 Outline of Last Lecture I. IntroductionII. ChromosomesIII. The Cell CycleIV. MitosisV. MeiosisVI. Life CyclesVII.Vocabulary and Sample Question from LectureOutline of Current Lecture I. Brief History of Mendel and DarwinI. Mendel’s ExperimentA. The Experiment and 4 PostulatesB. Methods of AnalysisII. Mathematical RulesIII. StatisticsA. Chi-square, degrees of freedom, and the p-valueB. Interpreting these resultsIV. Vocabulary and Sample QuestionsCurrent LectureI. History of MendelMendel began experimentation with peas in 1856, published his work in 1866 where it was ignored for 36 years, and finally in 1900: three scientists independently rediscovered Mendel’s laws of inheritanceDarwin’s Flaw: believed in “blending inheritance” and “Lamarckism”, both are incorrect. Thus Darwin’s theory of evolution by natural selection did not explain the source of genetic variationWhy? Four reasons: 1) He was not subscribed to Mendel’s work 2) The period of Darwin’s theory was too close to Mendel’s death 3) Mendel’s theory was not well understood by others 4) Mendel had few citations and was not recognizedMendel’s Flaw: had read Origin of the Species, but believed in hybridization instead of evolution,not knowing that his own findings would disprove this theoryII. Mendel’s ExperimentWhy did it succeed?1) Chose a good model organism (peas) 2) Chose good traits to study 3) Used statistics1. Why are peas a good model organism?You can control the mating process by avoiding self-pollination by manually removing the anthers or you could manually transfer pollen to stigma of other desired pea flowers2. Why are those traits good to study (aka are “Mendelian traits”)?Because they are single gene inherited phenotypes. These are easy to study and you can conduct a monohybrid cross.A. The ExperimentCrossed first two parents (P1) and found that all progeny (F1 generation) had the same trait.Note: True, whether selfed or cross-pollinatedHe crossed the (F1) generation to find a 3:1 ratio of two different phenotypes in the (F2)Found that each parent in the P1 cross donated one allele during gamete formation, but when fertilized, only one phenotype would be visibleThus: Formed Mendel’s 4 Postulates of Inheritance1) Unit factors in Pairs (aka genes)2) Dominance/recessive-ness3) Segregation – the paired unit factors segregate randomly so that each gamete receives one or the other with equal chance4) Independent Assortment – of segregating pairs of genesMendel found that there must be single units of inheritance, in which some traits dominated over others, and there was segregation in that the genotypes were “halving”Mendel’s Postulates in relation to chromosome behavior:1) Genes are part of the chromosomes, homologous chromosomes are paired2) Dominance/recessiveness doesn’t apply to chromosome behavior3) Each pair (the homologs) separates in meiosis4) Segregation – the paired unit factors segregate randomly so that each gamete receives one or the other with equal chanceB. Methods of AnalysisKnow how to create a Punnett Square. Note: each square filled out represents fertilization!How to perform a testcross: The organism of the dominant phenotype but unknown genotype iscrossed with a homozygous recessive individual. The ratios of the progeny phenotypes reveal the genotypeThere are two methods for analyzing cross involving multiple contrasting traits:#1) Dihybrid Cross – a cross involving two pairs of contrasting traits, can make 4 types of gametes from parents, resulting in a 9:3:3:1 ratio as a result of fertilizationNote: These may appear confusing but if you compare traits separately, 3:1 ratio persistsEx: (Yellow, round) x (green, wrinkled) gives an F2 ratio of:9/16 : yellow, round3/16 : green, round3/16 : yellow, wrinkled1/16 : green, wrinkledHowever if you compared only yellow vs. green, see a !2:4 = 3:1 ratioThus they individually show Mendel’s law of segregation.#2) The Forked-line Method, using an example of a trihybrid cross:III. Mathematical rulesAssuming independent assortment:n = number of gene pairs, 2n = number of different gametes, 3n = number of different genotypes, 2n = number of different phenotypes (assuming operational dominance)There are four Laws of Probability:1) Product Law – to find probability that several independent events occur simultaneously2) Sum Law – to find probability that at least one of several mutually exclusive events occur3) Conditional Probability – chance of event B given occurrence of A:P(A,B) = P(A) x P(B|A), and if A and B are independent, = P(A) x P(B)4) Binomial Theorem - use to find probability of m given n “tosses of a coin” if a = probability of m is known (for one coin toss), see book for equationIII. StatisticsRecall Mendel’s four postulates; postulates 3 and 4 are affected by random fluctuation.A. Chi-square, degrees of freedom, and the p-valueNull hypothesis – there is no difference between the observed and expected results. To analyze this, must know how to take a chi-square, find the degrees of freedom, and find p-value from table: Use a chi-square test to analyze this differenceEx: Your F2 generation was observed to have 787 tall plants, 277 dwarf plants. Expected value is a 3:1 ratio, thus the expected values are 798 tall plants and 266 dwarf plants. How much of a significant difference is this? ANS: x2 = (782 -798)2/798 + (277-266)/266 = 0.607Degrees of freedom (df) = number of categories – 1Ex: There are two categories: tall and dwarf. Thus, df = 2 -1 = 1P-value – the percentage of trials expected to deviate by chance as great or greater than what was seen in the initial valueWith chi-square value and degrees of freedom, simply use table (will be given) to get p-value:B. Interpreting these resultsRejecting the null hypothesis: If p < 5%, the deviation of the observed value from the expected is unlikely due to chanceIf null hypothesis rejected:1) Hypothesis is incorrect2) Hypothesis correct, assumptions made are incorrectIf null hypothesis accepted: 1) Hypothesis is correct2) Hypothesis is incorrect and not rejected because lack of statistical power(statistical power is related to sample size of population, error, etc…)IV. Vocab and Sample Questions from LectureCrosses – controlled mating whose progenies may show single gene inheritance patternsMutants – individual organisms having an altered form of a normal/most frequent property (which is