6.1.2 Continuing to Link Genes to Chemicals: Muller, Beadle, and Tatum

Question 1

note

Answer 1

• In the 1920s, the work of Hermann Muller and Thomas Hunt Morgan greatly furthered the field of genetics. Muller discovered that he could increase the mutation rate in fruit flies by subjecting them to x rays.
  • George Beadle and Edward Tatum subjected the red bread mold, Neurospora crassa, to x rays, greatly increasing the mutation rate. Normally, the mold can synthesize almost all of the organic compounds that it needs and can be grown on minimal medium that contains a few minerals, a single vitamin, and an energy source such as sucrose.

Question 2

Muller

Answer 2

• subjected fruit flies to x rays, causingmutations. The
  temperature also had an effect on the mutation rate. An
  increase in temperature of 10 degrees Celsius doubled the mutation rate.

Question 3

Beadle and Tatum’s experimental work

Answer 3

• Spores of Neurospora crassa were subjected to x rays. The spores are placed on enriched media containing all of the amino acids and allowed to grow until they, in turn, produce spores that are collected.
• The spores are grown on minimal media. If the spores can’t grow on the minimal media, then a mutation has occurred because of the x rays.
• Pieces of mutant mold are put in tubes containing minimal media plus one amino acid each. The mutant strain shown here can only grow when the amino acid alanine is present in the tube.
• The experimental results indicated that a genetic mutation could be linked to a defect in a specific enzyme.

Question 4

In their experiments, Beadle and Tatum used minimal media to

Answer 4

• pinpoint errors in specific metabolic pathways

Question 5

Beadle and Tatum designed their experiments to test whether

Answer 5

• mutations in the genetic material resulted in defective enzymes

Question 6

Beadle and Tatum’s experiments with Neurospora crassa connected

Answer 6

• mutations with enzymes

Question 7

Based on Beadle and Tatum’s conclusions, what would be the next logical experiment?

Answer 7

• Test what molecule is the genetic material, starting with the two most likely candidates

Question 8

At the time Beadle and Tatum began their work on Neurospora sp., scientists believed that

Answer 8

• Defects in enzymes had a hereditary component