1Two lociAA/AA x BB/BBAB/AB(F1)A AA Along chromshort chromlocus 1locus 2Parent AB BB Blong chromshort chromlocus 1locus 2Parent BLocus1/Locus 2AB/AB x AB/AB(F2)16 possibilitiesTwo loci, incomplete dominance(new and improved)2-locus interactionEffectof J atlocus 2Effect of variation at locus 2 depends on genotype atlocus 1: non-additiveFor example: locus 2 is polymorphism in a transcription factor gene that affects protein binding affinity, locus 1 is in abinding siteNO progeny as extreme as diploid hybridLab parent Pathogenic parentNO progeny as extreme as diploid hybridDiploid hybridTested in hybrid diploidsDifferentinsequenceLabPathogenicLabPathogenic2One mutant gene…From pathogenic strainOne mutant gene…From pathogenic strainFrom lab strainTwo mutant genes…From lab strainFrom pathogenic strainTwo mutant genes…From pathogenic strainFrom lab strainTwo mutant genes…From pathogenic strainFrom lab strainAgain, diploid with thisgene from thepathogenic strain growsBETTER at high T.Three mutant genesFrom lab strainDiploid with this genefrom the pathogenicstrain grows WORSEat high T!From pathogenic strain3Three mutant genesFrom pathogenic strainFrom pathogenic strainFrom pathogenic strainThree mutant genesFrom pathogenic strainFrom pathogenic strainFrom pathogenic strainThree mutant genesFrom pathogenic strainFrom pathogenic strainFrom pathogenic strainAlleles from thesame strain atdifferent genes/locican have differenteffects.Three mutant genes in same “locus”Three mutant genes in same “locus”Three mutant genesSo why did 0/900 haploid progeny havea phenotype as extreme as the diploidhybrid?4Lab parent Pathogenic parentNO progeny as extreme as diploid hybridDiploid hybridLab parent Pathogenic parentNO progeny as extreme as diploid hybridDiploid hybridLinked mutations of opposite effectPathLinked mutations of opposite effectPathLabLinked mutations of opposite effectPathLabVery unlikely“Multiple linked loci”5Model organism to humanWhy pigmentation?• Camouflage• Sexual selection• Protection from UV• Controlling light scatter• (Sunlight for vitamin D)• Accident—something else selected for nearbyGolden mutationGolden mutationMelanosomes, melanin-producing organellesGolden mutation1981: original mutant arose spontaneously in thelab.Showed mendelian segregation (1 locus), and isrecessive.Golden mutation1981: original mutant arose spontaneously in thelab.Showed mendelian segregation (1 locus), and isrecessive.Dramatic, single-locus differences not common inthe wild. Why not?6Linkage analysis with sparse markers mappedgolden to markers on chromosome 18, but high-resolution position of markers unknown.Linkage analysis with sparse markers mappedgolden to markers on chromosome 18, but high-resolution position of markers unknown.Genome sequence not completed…Linkage analysis with sparse markers mappedgolden to markers on chromosome 18, but high-resolution position of markers unknown.Genome sequence not completed…Hybrid cell lines not available…Library screenNative WT chromosomesShear, ligateLibrary screenNative WT chromosomes Genomic libraryShear, ligateLibrary screenNative WT chromosomes Genomic libraryShear, ligateHybridize to marker oligoDNA containing chr 18 marker85 kb7Fine-mappingInject into golden larvae85 kbFine-mappingInject into golden larvae85 kbFine-mappingGolden uninjectedInject into golden larvae85 kbFine-mappingInject into golden larvaeGolden uninjectedWT uninjected85 kbFine-mappingInject into golden larvaeGolden uninjectedWT uninjected85 kb“mosaic rescue”Fine-mapping85 kb8Fine-mapping85 kbslc24a5 mRNAFine-mappingInject into golden larvae85 kbslc24a5 mRNAFine-mappingInject into golden larvaeGolden uninjectedWT uninjectedGene is strongly conservedLooks likea Na/CaexchangepumpGene is strongly conserved*Looks likea Na/CaexchangepumpGene is strongly conserved** = premature stop codon in DNA of golden embryosLooks likea Na/Caexchangepump9Gene is strongly conserved** = premature stop codon in DNA of golden embryos(Don’t usually see such dramatic mutations in the wild)Looks likea Na/CaexchangepumpHuman can rescue fish!Human mRNA injectedHuman can rescue fish!Fish mRNA injectedGolden uninjectedHuman mRNA injectedWhat is this gene?melanophore (cell) markerslc24a5WTgolWhat is this gene?melanophore (cell) markerslc24a5WTgolCells themselvesare presentWhat is this gene?in mouse(QPCR)(cell line)10What is this gene? melanosome organelleWhat is this gene? melanosome organelleslc24a5Importance in humans?No truncation in humans, but…No truncation in humans, but…Which is the ancestral and which the derived allele?No truncation in humans, but…No other species have the Thr allele: what does this mean?11No truncation in humans, but…No other species have the Thr allele: what does this mean?Could be deleterious, just an accidental mutation.No truncation in humans, but…No other species have the Thr allele: what does this mean?Could be deleterious, just an accidental mutation.Could be advantageous for some humans, no other species.Population geneticsSurvey multiple European-Americans in Utah: >99% Thr.Population geneticsSurvey multiple European-Americans in Utah: >99% Thr.Survey multiple Han Chinese in Beijing: >93% Ala.Survey multiple Japanese in Tokyo: >93% Ala.Survey multiple Yoruba in Ibadan, Nigeria: >93% Ala.Population geneticsSurvey multiple European-Americans in Utah: >99% Thr.Survey multiple Han Chinese in Beijing: >93% Ala.Survey multiple Japanese in Tokyo: >93% Ala.Survey multiple Yoruba in Ibadan, Nigeria: >93% Ala.So this allele is NOT definining race.Population geneticsSurvey multiple European-Americans in Utah: >99% Thr.Survey multiple Han Chinese in Beijing: >93% Ala.Survey multiple Japanese in Tokyo: >93% Ala.Survey multiple Yoruba in Ibadan, Nigeria: >93% Ala.So this allele is NOT definining race.Does it explain differences in skin color in humans?12Correlates with human differences105 African-Carribeansand 203 African-Americans agreed to begenotyped and havemelanin contentmeasured.Correlates with human differencesAAAGGG105 African-Carribeansand 203 African-Americans agreed to begenotyped and havemelanin contentmeasured.ThrThr, AlaAlaCorrelates with human differencesAAAGGG105 African-Carribeansand 203 African-Americans agreed to begenotyped and havemelanin contentmeasured.Allele is rareThrThr, AlaAlaCorrelates with human differencesAAAGGGAllele is rarePerhaps explainsphenotypicvariation amongpeople of
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