Beadle and Tatum discovered several classes of Neurospora mutantsthat were able

Question

Beadle and Tatum discovered several classes of Neurospora mutantsthat were able to grow on
minimal medium with arginine added. Class I mutants were also ableto grow on medium (no
arginine) supplemented with either ornithine or citrulline, whereasclass II mutants could grow
on citrulline medium but not on ornithine medium. The metabolicpathway of arginine
synthesis is as follows:


Precursor ---> Ornithine ----> Citrulline ----->Arginine
                A                   B                     C
From these growth results, they could conclude that

a. One gene codes for the entire metabolic pathway
b. The genetic code of DNA is a triplet code
c. Class I mutants have their mutations later in the nucleotidechain than do class II
mutants, and thus have more functional enzymes
d. Class I mutants have a nonfunctional enzyme at step A, and classII mutants have a
nonfunctional enzyme at step B
e. Class I mutants have a nonfunctional enzyme at step B, and classII mutants have a
nonfunctional enzyme at step C



I will rate when the teacher graded my paper ,,,

Explanation / Answer

Well lets split the answer in two parts 1) The part one (class I mutants have a non functional enzymeat step A)-- though not derived from the observed data it in noway conflicts it. 2) The part two (class II mutants have a non functional enzymeat step B)-- is a direct conclusion from the observed data. Class II mutants did not have the ability to grow on ornithinemedium and thus had a non functional enzyme for the pathwayB. Hope this helps.

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