Tetrad analysisFig 5.15Nonparental = recombinantTetrad analysisWhat if two crossovers?A. Four recombinantsB. Two recombinantsC. No recombinantsFig 5.15Parental ≠ non-recombinantFig. 5.17Centromere is not a mutationFig. 5.21But you can still use it for mappingHow do we know that radiationcauses genetic defects?BridgesMullerMorganSturtevantMuller’s X-ray experiment (1928)Muller’s X-ray experimentCreated XClBMuller’s X-ray experimentCreated XClB XYMuller’s X-ray experimentCreated XClB•XYgametesMuller’s X-ray experimentCreated XClB•XY x XClBXgametesMuller’s X-ray experimentCreated XClB•XY x XClBX(Bar-eyed females)gametesMuller’s X-ray experimentCreated XClB•XY x XClBX•XX, •XXClB(ignore males)gametesMuller’s X-ray experimentCreated XClB•XY x XClBX•XX, •XXClBgametesMuller’s X-ray experimentCreated XClB•XY x XClBX•XX, •XXClBXY x •XXClBgametesMuller’s X-ray experimentCreated XClB•XY x XClBX•XX, •XXClBXY x •XXClB•XY, XClBY(ignore females)gametesMuller’s X-ray experimentCreated XClB•XY x XClBX•XX, •XXClBXY x •XXClB•XY, XClBY(lethal)gametesMuller’s X-ray experimentCreated XClB•XY x XClBX•XX, •XXClBXY x •XXClB•XY, XClBY(lethal)gametesHow many lethal mutations?Muller’s X-ray experiment11.5487.3240.0830% matingswith 0 malesTime irrad(min)•XY, XClBY(lethal)How many lethal mutations?Muller’s X-ray experiment11.5487.3240.0830% matingswith 0 malesTime irrad(min)Nobel prize to Muller, 1946: “for the discovery of theproduction of mutations by means of X-ray irradiation”•XY, XClBY(lethal)How many lethal mutations?Important for radiation biology,but also for basic geneticsGeorge Beadle & Edward Tatum(1941)Do mutations affect biochemistry oronly death, wing shape, pea color,etc?Bread moldFig. 5.14Beadle & TatumComplete med Minimal medBeadle & TatumComplete med Minimal med(why?)Beadle & TatumComplete med Minimal medComplete medBeadle & TatumComplete med Minimal medComplete med Minimal medBeadle & TatumComplete med Minimal medComplete med Minimal medMinimal + alanineBeadle & TatumComplete med Minimal medComplete med Minimal medMinimal + serineBeadle & TatumComplete med Minimal medComplete med Minimal medMinimal + B6Beadle & TatumComplete med Minimal medComplete med Minimal medMinimal + B6What’s wrong with the strain?A. It can use everything but B6B. It can make everything but B6C. It can grow on everything but B6Beadle & TatumComplete med Minimal medComplete med Minimal medMinimal + B6(what is a vitamin?)Beadle & TatumComplete med Minimal medComplete med Minimal medMinimal + B6pdx strainBeadle & TatumBeadle & TatumBeadle & TatumNow…how many mutations cause pdx?Beadle & Tatumpdx x WT(Haploid)(Haploid)Beadle & Tatumpdx x WT(if single-gene,what do weexpect?)Beadle & Tatumpdx x WTBeadle & Tatumpdx x WTBeadle & Tatumpdx x WTBeadle & Tatumpdx x WTBeadle & Tatumpdx x WTBeadle & TatumFailure to make B6 segregates 1:1Beadle & TatumFailure to make B6 segregates 1:1mutation in a single geneso…Beadle & TatumFailure to make B6 segregates 1:1mutation in a single geneStep in B6 synthesis attributed to a single gene“One-gene-one-enzyme”so…so…Beadle & TatumFailure to make B6 segregates 1:1mutation in a single geneNobel prize to Beadle & Tatum, 1958: “for theirdiscovery that genes act by regulating definitechemical events”so…so…Beadle & TatumNot quite one-gene-one-enzyme:“One-gene-one-polypeptide”Fig.
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