MENDELIAN GENETICSOBJECTIVESGENETICSGENETICS TERMINOLOGYMENDELHISTORICAL HYPOTHESES REGARDING INHERITANCEMENDELMENDEL’S CROSSESSlide 9Slide 10Slide 11MENDEL’S PEA PLANTSSlide 13Slide 14CROSS-POLLINATIONSlide 16Slide 17Slide 18MENDEL’S CONCLUSIONSMENDEL’S SYMBOLSPUNNETT SQUAREMENDEL’S CROSS OF PURE LINE PEA PLANTSMENDEL’S CROSS OF F1 PLANTSPOSSIBLE GENOTYPESPROBABILITY THEORYSlide 26MENDEL’S SYMBOLSSlide 28PUNNETT SQUARE FOR TWO TRAITSSlide 30MENDEL’S LAW OF INDEPENDENT ASSORTMENTINDEPENDENT ASSORTMENTTHE TEST CROSSSlide 34CONCLUSIONS: MENDELIAN GENETICSMENDELIAN GENETICSOBJECTIVES•Understand Mendel’s principles governing genetics•Understand meaning of relevant vocabulary•Predict results of mono/dihybrid crosses using Punnett square•Know exceptions to rulesGENETICS•Genetics:•Heredity:GENETICS TERMINOLOGYGene (Character):Locus (loci= pl.): Allele (Trait): Genotype: Phenotype:MENDEL•Gregor Mendel–Interested in basic patterns governing the transmission of traits from parent to offspring–Mendel’s work precedes an understanding of meiosis/genes/chromosomesHISTORICAL HYPOTHESES REGARDING INHERITANCEBlending Inheritance Hypothesis:Inheritance of Acquired Characteristics HypothesisMENDEL•Mendel performed crosses between pure bred garden peas•Began studying inheritance of ONE trait•Later, multiple traits studied togetherMENDEL’S CROSSES•Mendel's plants had two observable “forms” (alleles) of each “character” (gene)–Green or Yellow seeds• Round or Wrinkled seedsTraitForms of Trait (Phenotype)Seed shapeRoundWrinkledSeed colorPod shapePod colorYellowGreenInflatedGreenConstructedYellowRoundWrinkledYellow GreenSmooth ConstrictedGreenYellowororororTrait Forms of Trait (Phenotype)Flower colorPurple WhiteAxial (on stem) Terminal (at tip)Flower andpod positionStem lengthTall DwarfPurpleWhiteAxial (on stem) Terminal (at tip)DwarfTallorororMENDEL•Looked at traits exhibited by progeny of crosses–Found observable evidence of how parents transmit traits to offspringMENDEL’S PEA PLANTS•Pisum sativumStigma (receives pollen)Anthers(produce pollengrains, whichcontain malegametes)Ovules (produce female gametes)Male parts = anthers–Pollen grain contain spermFemale parts = pistil–Ovule = eggsSELF FERTILIZATIONMENDEL’S PEA PLANTSControlled Mating:–Cut off reproductive organ to stop self fertilization–Cross fertilize plants in a controlled fashion–Plant that contributes pollen –Plant that receives the pollenCROSS-POLLINATIONCROSS-POLLINATION1. Remove anthersfrom one plant.2. Collect pollenfrom a different plant.3. Transfer pollento stigma of the 1st plant(plant without anthers)MENDEL’S CROSSESRound ParentWrinkl ed ParentxMENDEL’S CROSSESNext, Mendel crossed F1 (bro-sis mating): Round (F1) Round xMENDEL’S CROSSESMendel Determines (Phenotypic) Ratio: F2: 5474 Round : 1850 Wrinkl ed –Similar pattern observed in other 6 traitsMENDEL’S CONCLUSIONSMENDEL’S SYMBOLS•Mendel assigned symbols to hereditary characters•Letters represent versions of a gene (alleles):–Ex: If Letter “r” represents a gene then:PUNNETT SQUARE•R.C. Punnett–Leading geneticist in early 1900s–Invented technique called the “Punnett Square”–Place gamete possibilities for 2 parents along axes –Internal boxes represent union of gametes –Used to predict genotype and phenotype of potential zygoteMENDEL’S CROSS OF PURE LINE PEA PLANTS PARENT: R RPARENT: r r** hint: gametes along top, “whole people” on insideR is roundr is wrinkledMENDEL’S CROSS OF F1 PLANTS• Phenotypic Ratio: • Genotypic RatioCrossing the F1s: Rr x RrR = roundr = wrinkledPOSSIBLE GENOTYPESThree possible genotypes for each gene in a diploid cell:•Homozygous:•Homozygous Dominant: •Homozygous Recessive: •Heterozygous:PROBABILITY THEORYIn Diploid Organisms, •Each allele has 50% chance of being found in a particular gamete •To calculate likelihood of two alleles combining (i.e. fertilization):MENDEL’S CROSSES•Dihybrid Crosses:–Mendel used pea plants to follow inheritance of TWO traits •Another pattern began to emerge…MENDEL’S SYMBOLS•Seed Shape:•R is dominant allele (Round)•r is recessive allele (Wrinkled)•Seed Color:•Y is dominant allele (Yellow)•y is recessive allele (Green)F2 generationphenotypeMendel’sNumbers315101 108 32 = 556Fraction ofprogeny9/16 3/16 3/16 1/16 = 1F2 OFFSPRING FROM DIHYBRID CROSSNote: New mixtures of traits are observed in F2!!PUNNETT SQUARE FOR TWO TRAITSDo genes segregate into gametes together or independently?PUNNETT SQUARE FOR TWO TRAITSIf genes segregate independently of each other, we end up withMENDEL’S LAW OF INDEPENDENT ASSORTMENT•Law of Independent Assortment:INDEPENDENT ASSORTMENTORDuring meiosis I, homologs can line up two different ways before separating.Brown eyesBlack hairRed hairBlue eyesTHE TEST CROSS•To determine genotype of an individualMENDELWhy Mendel Was Successful:•Unbiased•Selected good model organism•Used pure breeds as parents•Large sample size•Quantitative analysis•Controlled experiments•Studied obvious traitsCONCLUSIONS: MENDELIAN