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Tetrad analysis. Fig 5.15. Nonparental = recombinant . Tetrad analysis. What if two crossovers?. Four recombinants Two recombinants No recombinants. Fig 5.15. Parental ≠ non-recombinant. Fig. 5.17. Centromere is not a mutation. But you can still use it for mapping. Fig. 5.21.

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Tetrad analysis

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Tetrad analysis

Fig 5.15

Nonparental = recombinant


Tetrad analysis

What if two crossovers?

Four recombinants

Two recombinants

No recombinants

Fig 5.15


Parental ≠ non-recombinant

Fig. 5.17


Centromere is not a mutation

But you can still use it for mapping

Fig. 5.21


How do we know that radiation causes genetic defects?


Morgan

Bridges

Muller

Sturtevant


Muller’s X-ray experiment (1928)


Muller’s X-ray experiment

Created XClB


Muller’s X-ray experiment

Created XClB

XY


Muller’s X-ray experiment

Created XClB

•XY

gametes


Muller’s X-ray experiment

Created XClB

•XY x XClBX

gametes


Muller’s X-ray experiment

Created XClB

•XY x XClBX

(Bar-eyed females)

gametes


Muller’s X-ray experiment

Created XClB

•XY x XClBX

gametes

•XX, •XXClB

(ignore males)


Muller’s X-ray experiment

Created XClB

•XY x XClBX

gametes

•XX, •XXClB


Muller’s X-ray experiment

Created XClB

•XY x XClBX

gametes

•XX, •XXClB

XY x •XXClB


Muller’s X-ray experiment

Created XClB

•XY x XClBX

gametes

•XX, •XXClB

XY x •XXClB

•XY, XClBY

(ignore females)


Muller’s X-ray experiment

Created XClB

•XY x XClBX

gametes

•XX, •XXClB

XY x •XXClB

•XY, XClBY

(lethal)


Muller’s X-ray experiment

Created XClB

•XY x XClBX

gametes

•XX, •XXClB

XY x •XXClB

•XY, XClBY

How many lethal mutations?

(lethal)


Muller’s X-ray experiment

•XY, XClBY

How many lethal mutations?

(lethal)


Muller’s X-ray experiment

•XY, XClBY

How many lethal mutations?

(lethal)

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

Complete med


Beadle & Tatum

Complete med

Minimal med

Complete med

Minimal med


Beadle & Tatum

Complete med

Minimal med

Complete med

Minimal med

Minimal + alanine


Beadle & Tatum

Complete med

Minimal med

Complete med

Minimal med

Minimal + serine


Beadle & Tatum

Complete med

Minimal med

Complete med

Minimal med

Minimal + B6


Beadle & Tatum

Complete med

Minimal med

Complete med

Minimal med

What’s wrong with the strain?

It can use everything but B6

It can make everything but B6

It can grow on everything but B6

Minimal + B6


Beadle & Tatum

Complete med

Minimal med

Complete med

Minimal med

(what is a vitamin?)

Minimal + B6


Beadle & Tatum

Complete med

Minimal med

Complete med

Minimal med

pdx strain

Minimal + B6


Beadle & Tatum


Beadle & Tatum


Beadle & Tatum

Now…how many mutations cause pdx?


Beadle & Tatum

pdx xWT

(Haploid)

(Haploid)


Beadle & Tatum

(if single-gene, what do we expect?)

pdx xWT


Beadle & Tatum

pdx xWT


Beadle & Tatum

pdx xWT


Beadle & Tatum

pdx xWT


Beadle & Tatum

pdx xWT


Beadle & Tatum

pdx xWT


Beadle & Tatum

Failure to make B6 segregates 1:1


Beadle & Tatum

Failure to make B6 segregates 1:1

so…

mutation in a single gene


Beadle & Tatum

Failure to make B6 segregates 1:1

so…

mutation in a single gene

so…

Step in B6 synthesis attributed to a single gene

“One-gene-one-enzyme”


Beadle & Tatum

Failure to make B6 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”


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