The following figure represents experimental results from study designed after t

Question

The following figure represents experimental results from study designed after the Beadle and Tatum experiment.  

Assume the mutants are homozygous for recessive alleles causing their phenotypes.

a. Create an ordered pathway of nutrients and mutants (pull down the correct mutant for M1-M4 and the correct nutrient for Nut1-Nut4):

b. If you crossed mutants 2 and 5, what would the nutrient requirements of the offspring be?

c. If you crossed mutants 2 and 4, what would the nutrient requirements of the F1 be?

d. If you conducted an F1xF1 cross, what would the phenotypic ratios of the F2 be?

Nutrient A Nutrient B Nutrient C Nutrient D Mutant 1 Yes No Yes Yes Mutant 2 No No Yes Yes Mutant 3 Yes Yes Yes Yes Mutant 4 No No Yes No Mutant 5 No No Yes Yes

Explanation / Answer

Beadle and Tatum stated the one gene one enzyme concept. According to them, one gene dictates the synthesis of an enzyme. Later on, it was modified that one gene directs the synthesis of a polypeptide which can form an enzyme or become the component of an enzyme.

As is seen in the figure, mutant 4 grows only in the presence of nutrient C and none else. So, nutrient C must help in the formation of ultimate product of gene expression. Mutants 2 and 5 have alike results. They grow in the presence of nutrients C and D. So, nutrient D must be the precursor of nutrient C.

Mutant 1 grows in all the nutrients A, C and D, leaving only nutrient B. So, the precursor of nutrient D must be nutrient A. Mutant 3 grows in all four nutrients. So, nutrient B is the precursor of nutrient A.

Therefore, the order is somewhat like this:

Precursor ----> Mutant 3 ----> Nutrient B; Mutant 1 ----> Nutrient A; Mutant 2/5 ----> Nutrient D; Mutant 4 ----> Nutrient C.  

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