Presentation on theme: "Gregor Mendel “Father of Genetics”"— Presentation transcript:
1 Gregor Mendel “Father of Genetics” Mendelian GeneticsWhile assigned to teach, he was also assigned to tend the gardens and grow vegetables for the monks to eat.Augustinian Monk at Brno Monastery in Austria (now Czech Republic)Not a great teacher but well trained in math, statistics, probability, physics, and interested in plants and heredity.Mountains with short, cool growing season meant pea (Pisum sativum) was an ideal crop plant.Gregor Mendel“Father of Genetics”
2 Contributions in 1860s (US Civil War Era) Discovered Genes as Particles of InheritanceDiscovered Patterns of InheritanceDiscovered Genes Come from Both ParentsEgg + Sperm = ZygoteNature vs NurtureSperm means Seed (Homunculus)Discovered One Form of Gene (Allele) Dominant to AnotherDiscovered Recessive Allele Expressed in Absence of Dominant Allele
3 Mendel worked with peas (Pisum sativum) Good choice for environment of monasteryNetwork provided unusual varieties for testingObligate self-pollination reproductive systemPermits side-by-side genetic barriersCross-pollinations require intentional processCrosses meticulously documentedCrosses numerically/statistically analyzedScientists of 1860s could not understand mathWork lost in journals for 50 years!Rediscovered in 1900s independently by 3 scientistsRecognized as landmark work!
4 One Example of Mendel’s Work TallxDwarfPhenotypePDDddGenotypeHomozygousDominantHomozygousRecessiveAll TallClearly Tall is Inherited…What happened to Dwarf?F1DdTall is dominant to DwarfUse D/d rather than T/t for symbolic logicHeterozygousF1 x F1 = F2possible gametesPunnett Square:Dd3/4 Tall1/4 DwarfF2DTallDDTallDdpossible gametesdTallDdDwarfddDwarf is not missing…just masked as “recessive” in a diploid state… there IS a female contribution.
5 Mendel as a Scientist F2 F1 x F1 = F2 Test Cross: Unknown Tall x Dwarf ddTallDddDDDPunnett Square:possible gametesTest Cross:Unknown TallxDwarfddpossible gametesIf Unknown is DD:ddDTallDdTallDdpossible gametesTest Progeny All TallDTallDdTallDd1/3 of F2 Tall are DD2/3 of F2 Tall are Ddpossible gametesIf Unknown is Dd:ddDTallDdTallDdpossible gametesTest Progeny Half Tall Half DwarfdDwarfddDwarfdd
6 Another Example of Mendel’s Work GreenxYellowPhenotypePggGGGenotypeHomozygousRecessiveHomozygousDominantAll YellowClearly Yellow is Inherited…What happened to Green?F1GgYellow is dominant to GreenUse G/g rather than Y/y for symbolic logicHeterozygousF1 x F1 = F2possible gametesNEVER use G/Y or g/yPunnett Square:Gg3/4 Yellow1/4 GreenF2GYellowGGYellowGgpossible gametesgYellowGgGreenggGreen is not missing…just masked as “recessive” in diploid state
7 Mendel as a Scientist F2 F1 x F1 = F2 Test Cross: Unknown Yellow x GreenggYellowGggGGGPunnett Square:possible gametesTest Cross:Unknown YellowxGreenggpossible gametesIf Unknown is GG:ggGYellowGgYellowGgpossible gametesTest Progeny All YellowGYellowGgYellowGg1/3 of F2 Yellow are GG2/3 of F2 Yellow are Ggpossible gametesIf Unknown is Gg:ggGYellowGgYellowGgpossible gametesTest Progeny Half Yellow Half GreengGreenggGreengg
8 You could be wrong (rarely)! Unknown YellowGreenxMendel as a ScientistggYellowGgGgpossible gametesTest Cross:If Unknown is GG:If Unknown is Gg:Actual ResultsDecision3 Yellow 2 GreenGg2 Yellow 3 GreenGg1 Yellow 4 GreenGgSmall families do not follow expected ratios perfectly!0 Yellow 5 GreenGgRare, but it can happen!4 Yellow 1 GreenGgIt only takes 1 green to be sure the unknown is Gg!5 Yellow 0 GreenGG<5% chance unknown is Gg1/2 • 1/2 • 1/2 • 1/2 • 1/2 = 1/32You could be wrong (rarely)!
9 Genetics After Mendel P F1 F2 Red Yellow x PRPR PYPY All Orange PRPY After 1900 several scientists tried to replicate Mendel’s crosses using other species including snapdragon.Genetics After MendelRedYellowPxPRPRPYPYWhen these alleles go walking, they both do some talking (codominance)!OK, so we cannot use R/r nor Y/y so we pick a third letter…P for the petal color gene.Notice: we do NOT mix R/Y or r/y!All OrangeF1PRPYF1 x F1 = F2possible gametesPunnett Square:PRPYF2PRRedPRPROrangePRPYThis F2 will NOT have a 3:1 ratio of phenotypes.Instead it shows a 1:2:1 ratio!The exception here proves the rule.possible gametesPYOrangePRPYYellowPYPY
10 Recessive can be common! In addition to this, there are multiple alleles possible:PR = red PY = yellow p = no pigmentThe combination of alleles in a diploid determine the flower color:PRPR = redPRPY = orangePYPY = yellowPRp = pinkPYp = creampp = whiteHuman hair color follows a similar pattern:Alleles: HBn = brown HBd = blonde hR = red hbk = blackThe combinations of these alleles determine the base hair color:HBnHBn = dark brownHBnHBd = sandy brownHBnhR = auburnHBnhbk = dark brownHBdHBd = blondeHBdhR = strawberry blondeHBdhbk = blondehRhR = redhRhbk = redhbkhbk = blackRecessive can be common!Dominant does NOT mean frequent!
11 Another Example of Recessive Being Common: Pisum sativum Garden Peas: green seed, wrinkled seed, dwarf stature, white flowerggwwddaaIn other words: a quadruple double-recessiveis the most common garden pea on Earth!Quantitative Inheritance: multiple genes control traitHighest Crop Yield: AABBCCDDEEIntermediate Crop Yield: AabbCCDdEeLowest Crop Yield: aabbccddeeDarkest Skin Color: AABBCCDDEEIntermediate Skin Color: AaBbCcDdEeLightest Skin Color: aabbccddeeAaBbCcDdEe x AaBbCcDdEe can produce a huge range of colors!Yet TV talk show guests argue this point for Maury, etc.
12 Phenotype = Genotype + Environment but everyone can have “tan lines.” Crop Yield = Genotype+ Minerals+ Water+ Light- Pestsetc.Optimizing these factors determines agricultural productivity…last part of our course!Human Skin Color = Genotype+ Sun (UV) Exposure- Aging FactorsThe sun exposure effect is most obvious in people of intermediate skin base colorbut everyone can have “tan lines.”
13 “Half-breed” is better Who Gets To Mate With Whom? …Two ExtremesInbreeding Depression: related parents give same recessives to childrenHemophilia: Queen Victoria’s Mutation and Diseased GrandchildrenTay-Sachs: Jewish PopulationsBipolar: Irish PopulationsDog Diseases: German Shepherd hip dysplasiaIncest Taboo…butHybrid Vigor: recessives of one family are “covered” by dominant of other familyWild Corn A x Wild Corn B“Half-breed” is betterHigh Yield Hybrid Corn!Are Human Cultures of “Great Melting Pots” Superior?“Mutt” is best dog!
14 Mechanisms Preventing Inbreeding in Plants Evolution of Unisexuality: Dioecious Holly and KiwiCommon Gardener Error at Nursery PickupTiming Separation of BisexualityProtandry: Male First, Then Female (Alstromeria, Campanula)Protogyny: Female First (Oenothera)Sequence in Cucumis: Male, Bisexual, Female, ParthenocarpicSelf-Incompatibility: Sweet Cherry, Almond, Filbertpollen germination preventedpollen tube growth haltedsynergid action (sperm release) preventedsperm deactivated
15 Going Outside the Box of a Species: Bread Wheat AA (diploid wheat) x DD (diploid grass)Triticum urartuAegilops tauschiiAD (sterile diploid)similar to mule!colchicineor spontaneousAADD (fertile tetraploid)BB (diploid grass)Aegilops speltoidesBBAADDFertile hexaploidBread WheatTriticum aestivumcolchicineor spontaneousBAD (sterile triploid)Bread Wheat Created 7500 BC with spontaneous doubling of DNALevy A. A. and M. Feldman The impact of polyploidy on grass genome evolution. Plant Physiol. 130:
16 Yet Another Example of Mendel’s Work WrinkledxRoundPhenotypePwwWWGenotypeHomozygousRecessiveHomozygousDominantAll RoundRound is dominant to WrinkledUse W/w rather than R/r for symbolic logic: in handwriting make it legible! WwF1WwHeterozygousF1 x F1 = F2NEVER use W/R or w/rpossible gametesPunnett Square:WwF2WRoundWWRoundWw3/4 Round1/4 Wrinkledpossible gameteswRoundWwWrinkledww
17 Mendel as a Scientist F2 F1 x F1 = F2 Test Cross: Unknown Round x WrinkledwwRoundWwwWWWPunnett Square:possible gametesTest Cross:Unknown RoundxWrinkledwwpossible gametesIf Unknown is WW:wwWRoundWwRoundWwpossible gametesTest Progeny All RoundWRoundWwRoundWwpossible gametesIf Unknown is Ww:wwWRoundWwRoundWwpossible gametesTest Progeny Half Round Half WrinkledwWrinkledwwWrinkledww
18 You could be wrong (rarely)! Mendel as a ScientistActual ResultsDecisionTest Cross:3 Round 2 WrinkledWwUnknown RoundxWrinkledww2 Round 3 WrinkledWwpossible gametesIf Unknown is WW:1 Round 4 WrinkledWwwwSmall families do not follow expected ratios perfectly!WRoundWwRoundWw0 Round 5 WrinkledWwpossible gametesRare, but it can happen!WRoundWwRoundWw4 Round 1 WrinkledWwIt only takes 1 wrinkled to be sure the unknown is Ww!possible gametesIf Unknown is Ww:ww5 Round 0 WrinkledWWWRoundWwRoundWw<5% chance unknown is Wwpossible gametes1/2 • 1/2 • 1/2 • 1/2 • 1/2 = 1/32wWrinkledwwWrinkledwwYou could be wrong (rarely)!
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