Presentation on theme: "Pleiotropy: One gene influences more than one trait"— Presentation transcript:
1 Pleiotropy: One gene influences more than one trait 1 Gene, 2 Alleles3 Genotypes2 Phenotypes:Shape and ColorPPPpppMapPhenotype: the observable physical state of an organism. Itsmorphology, physiology, and behavior.Genotype: the genetic state of an organism.
2 The Reason for Mendel’s Success Mendel discovered the MAP from Phenotype to Genotypebecause, for all 7 of Mendel’s traits in peas, the MAP was SIMPLE:2 Phenotypes GenotypesYYHomozygoteDominantYyHeterozygoteRecessiveyyHomozygoteMapdirectlyObservedtraitsindirectlyInferredgenes
4 BB Bb bb EE Ee ee Epistasis for Coat Color in the Laborador Retriever: Epistasis:Two (or more) genes interact to cause one phenotype.BBBbbbEEEeee
5 With Epistasis the Map from Genotype to Phenotype is COMPLEX Complex Map of Coat Color Trait to Multi-Gene Genotypes3 Phenotypes9 GenotypesBBEEBBEeBbEEBbEebbEEbbEeBBeeBbeebbee
6 Epistasis = Gene B’s Effect on phenotype, v, changes with the genotype at a Different Locus, E: BBbbBBbbEffect of B is Large+0.25Phenotypic Effect of BEffect of B is Small0.00EE eeBackground Genotype at the E locus
7 For most traits, the ENVIRONMENT also Affects the MAP between Phenotype and Genotype3 Phenotypes Environments 1 GenotypePoor NutritionAverage NutritionCCExcess NutritionThis variation in phenotype is caused by variation in theenvironment and NOT by variation in genotype
8 For Mendel there was No Effect of Environment: map of Genotype to Phenotype was constantso that Phenotypic Variationwas caused by Genotypic VariationYYYyPhenotype: Seed ColoryyCold Temperate HotEnvironmentEach line on this graph is called a “Norm of Reaction”::The range of phenotypes produced by ONE genotype when thatgenotype is reared across a series of different environments.
9 Most traits are affected by the Environment: which changes the Relationship of Genotype to PhenotypeCCPhenotype: SizePoor Average ExcessEnvironmentThe line on this graph is the “Norm of Reaction”for genotype CC: ONE genotype-THREE phenotypes
10 For most traits, the ENVIRONMENT Affects the MAP between Phenotype and Genotype3 Phenotypes Environments 3 GenotypesExcessCcPoorPoorAverageCCExcessExcessccThe Environment makes the MAP between Phenotype and GenotypeMany to Many instead of One to One.
11 Gene action makes the MAP between Phenotype and Genotype ExcessCcDDPoorPoorAverageCCDdExcessExcessccddGene action makes the MAP between Phenotype and GenotypeMany to Many instead of One to One:Pleiotropy: one gene affects two or more traits.Epistasis: two or more genes affect one trait.
12 Two phenotypes of the barnacle Chthamalus anisopomaBent morph - more resistant to snail predation,but less fecundStraight Morph – less resistant to snail predationbut more fecundBent morphStraight MorphTrade-off !!The predatory snailAcanthina angelica
13 For most traits, there are effects of Environment: which change the Relationship of Genotype to PhenotypePhenotype: Shell ShapeWithoutWithEnvironment
14 Temperature-dependent sex determination Barber’s Map Turtle, Graptemys barbouriPhoto: Steven FreedbergAdult Male Adult Female<28.5 °C >29.0 °CEnvironment of Egg determines Sex of the Turtle!
15 For Mendel, there was no effect of other Genes = Relationship of Genotype to Phenotype was ConstantYYYyPhenotype: Seed Coloryyww Ww WWGenetic Background at Another Gene
16 For Mendel, there was no effect of Environment = Relationship of Genotype to Phenotype was ConstantYYYyPhenotype: Seed Coloryycold intermediate hotEnvironments
17 AA Aa aa EE Ee ee AA Aa aa EE Ee ee For most traits, there are Pleiotropy, Epistasisand Environmental Effects on PhenotypeHot EnvironmentCold EnvironmentAAAaaaEEEeeeAAAaaaEEEeee
18 Effects of Environment and Epistasis and Pleiotropy greatly complicate Mapping of Genotype onto PhenotypeDifferent Phenotypes do not necessarily indicate Different Genotypes.Similar Phenotypes do not necessarily indicate Similar Genotypes.Environment and Epistasis and Pleiotropy make the MAP between Genotype and Phenotype Many-to-Many
19 How do we study a Many-to-Many Map of Genotype and Phenotype? We want to know “How much variation in a phenotype is caused by genetic differences among individuals?” (“nature”)We want to know “How much variation in a phenotype is caused by environmental differences among individuals?” (“nurture”)What are the environmental vs genetic causes of the differences in morphology, behavior, and physiology among individuals.
20 A Population with Phenotypic Variation among its Members Hot:A Population with PhenotypicVariation among its MembersTemperateDid Different EnvironmentsCause these differences in size?Cold:AAAAAADid Different GenotypesCause these differences in size?AaAaAaaaaaaa
21 Controlled Breeding Experiments Make crosses between different individuals and obtain offspring.Measure the morphology, behavior, physiology of each offspring.Estimate the genetic causes of the offspring variation by measuring the “degree of resemblance” among genetic relatives.Genetic Relatives: (1) Parent-Offspring, (2) Brother-Sister, (3) Half-Siblings (same father, different mothers).
22 Heredity is the Cause of Resemblance between Genetic Relatives Different kinds of relatives may share more or less phenotypic resemblance.Diploid Genetic Relatives:(1) Parent-Offspring: share ½ of their genes.(2) Brother-Sister: share ½ of their genes.(3) Half-Siblings (same father, different mothers): share ¼ of their genes.
23 Non-Genetic Causes of Resemblance among Genetic Relatives Similar environments: Genetic relatives often grow up in similar environments and individuals reared in the same environment may be more similar to one another than individuals reared in different environments.Maternal Effects: Mother is a “special environment,” she provides both genes and nutritional environment. In mammals, these effects begin in utero.
24 In nature, the MATERNAL ENVIRONMENT Affects the MAP between Phenotype and Genotype1 Phenotype MOM 2 GenotypesCcccSiblings are Similar GeneticallySiblings are Similar Environmentally (through mother)
25 Paternal Half-Sibs 1 x 2 3 4 5 6 2 x Half-sibs Of Male 2 Half-sibs Of Difference?Resemblance?Resemblance?
29 Half-sib Breeding Design: Environmental AND Genetic Effects 1x232x34510x282930E1E2E3
30 Difficulties with Human Genetics Cannot impose breeding designs on human population. Therefore cannot separate non-genetic maternal effects from genetic effects.Cannot rear offspring of same parents in different environments: Therefore cannot separate non-genetic environmental effects from genetic effects.Debate over “Nature vs Nurture” cannot be experimentally resolved in humans.
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