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. ClassI mutants were also able to grow on medium supplemented with eitherornithine or citrulline, wheareas class II mutants could grow oncitruline medium but not on ornithine medium. The metabolic pathwayof arginine synthesis is as follows:    Precursor->Ornithine->Citruline->Arginine       A    B    C
From the behavior of their mutants, Beadle and Tatum couldconclude that a. Class I mutants have a nonfunctional enzyme at stepA, andclass II mutants have a nonfunctional enzyme at step B. B. one gene codes for the entire metabolic pathway. c. class I mutants have a nonfunctional enzyme a step B, andclass II mutants have a nonfunctional enzyme at step C. d. the genetic code of DNA is a triplet code e. class I mutants have their mutations later in thenucleotide chain than do class II mutants and thus have morefunctional enzymes.    Precursor->Ornithine->Citruline->Arginine       A    B    C
From the behavior of their mutants, Beadle and Tatum couldconclude that a. Class I mutants have a nonfunctional enzyme at stepA, andclass II mutants have a nonfunctional enzyme at step B. B. one gene codes for the entire metabolic pathway. c. class I mutants have a nonfunctional enzyme a step B, andclass II mutants have a nonfunctional enzyme at step C. d. the genetic code of DNA is a triplet code e. class I mutants have their mutations later in thenucleotide chain than do class II mutants and thus have morefunctional enzymes.

Explanation / Answer

The answer is A because class 1 mutants have a defective enzyme atstep A while class 2 have a defective enzyme at step B. Thus, theycant produce Citruline but are able to use it as an intermediatewhen provided with it.

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