PowerPoint PresentationSlide 2Slide 3Slide 4How do we know that radiation causes genetic defects?Slide 6Muller’s X-ray experiment (1928)Muller’s X-ray experimentSlide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Important for radiation biology, but also for basic geneticsGeorge Beadle & Edward Tatum (1941)Bread moldBeadle & TatumSlide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Tetrad 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 radiation causes 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 experimentTime irrad (min)% matings with 0 males0 0.08324 7.348 11.5•XY, XClBY(lethal)How many lethal mutations?Muller’s X-ray experimentTime irrad (min)% matings with 0 males0 0.08324 7.348 11.5Nobel prize to Muller, 1946: “for the discovery of the production 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 or only death, wing shape, pea color, etc?Bread moldFig. 5.14QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Beadle & 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 we expect?)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 their discovery that genes act by regulating definite chemical events”so…so…Beadle & TatumNot quite one-gene-one-enzyme:“One-gene-one-polypeptide”Fig.
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