Tetrad analysis Fig 5 15 Nonparental recombinant Tetrad

Tetrad analysis Fig 5. 15 Nonparental = recombinant

Tetrad analysis What if two crossovers? Fig 5. 15 A. Four recombinants B. Two recombinants C. No recombinants

Parental ≠ non-recombinant Fig. 5. 17

Centromere is not a mutation Fig. 5. 21 But you can still use it for mapping

How do we know that radiation causes genetic defects?

Bridges Sturtevant Morgan Muller

Muller’s X-ray experiment (1928)

Muller’s X-ray experiment Created XCl. B

Muller’s X-ray experiment Created XCl. B XY

Muller’s X-ray experiment Created XCl. B • XY gametes

Muller’s X-ray experiment Created XCl. B • XY gametes x XCl. BX

Muller’s X-ray experiment Created XCl. B • XY gametes x XCl. BX (Bar-eyed females)

Muller’s X-ray experiment Created XCl. B • XY x XCl. BX gametes • XX, • XXCl. B (ignore males)

Muller’s X-ray experiment Created XCl. B • XY x XCl. BX gametes • XX, • XXCl. B

Muller’s X-ray experiment Created XCl. B • XY x XCl. BX gametes • XX, • XXCl. B XY x • XXCl. B

Muller’s X-ray experiment Created XCl. B • XY x XCl. BX gametes • XX, • XXCl. B XY x • XXCl. B • XY, XCl. BY (ignore females)

Muller’s X-ray experiment Created XCl. B • XY x XCl. BX gametes • XX, • XXCl. B XY x • XXCl. B • XY, XCl. BY (lethal)

Muller’s X-ray experiment Created XCl. B • XY x XCl. BX gametes • XX, • XXCl. B XY How many lethal mutations? x • XXCl. B • XY, XCl. BY (lethal)

Muller’s X-ray experiment How many lethal mutations? • XY, XCl. BY (lethal) Time irrad (min) % matings with 0 males 0 0. 083 24 7. 3 48 11. 5

Muller’s X-ray experiment How many lethal mutations? • XY, XCl. BY (lethal) Time irrad (min) % matings with 0 males 0 0. 083 24 7. 3 48 11. 5 Nobel prize to Muller, 1946: “for the discovery of the production of mutations by means of X-ray irradiation”

Important for radiation biology, but also for basic genetics

George Beadle & Edward Tatum (1941) Do mutations affect biochemistry or only death, wing shape, pea color, etc?

Bread mold Fig. 5. 14

Beadle & Tatum Complete med Minimal med

Beadle & Tatum (why? ) Complete med Minimal med

Beadle & Tatum Complete med Minimal med

Beadle & Tatum Complete med Minimal + alanine

Beadle & Tatum Complete med Minimal + serine

Beadle & Tatum Complete med Minimal + B 6

Beadle & Tatum Complete med Minimal med What’s wrong with the strain? A. It can use everything but B 6 B. It can make everything but B 6 C. It can grow on everything but B 6 Minimal + B 6

Beadle & Tatum Complete med Minimal med Complete med (what is a vitamin? ) Minimal med Minimal + B 6

Beadle & Tatum Complete med Minimal med pdx strain Minimal + B 6

Beadle & Tatum

Beadle & Tatum Now…how many mutations cause pdx?

Beadle & Tatum (Haploid) pdx x WT (Haploid)

Beadle & Tatum pdx x WT (if single-gene, what do we expect? )

Beadle & Tatum pdx x WT

Beadle & Tatum Failure to make B 6 segregates 1: 1

Beadle & Tatum Failure to make B 6 segregates 1: 1 so… mutation in a single gene

Beadle & Tatum Failure to make B 6 segregates 1: 1 so… mutation in a single gene so… Step in B 6 synthesis attributed to a single gene “One-gene-one-enzyme”

Beadle & Tatum Failure to make B 6 segregates 1: 1 so… mutation in a single gene so… Nobel prize to Beadle & Tatum, 1958: “for their discovery that genes act by regulating definite chemical events”

Beadle & Tatum Not quite one-gene-one-enzyme: Fig. 9. 1 “One-gene-one-polypeptide”