The work by Beadle and Tatum lead to the identification of arg-1, arg-2, and arg
ID: 171473 • Letter: T
Question
The work by Beadle and Tatum lead to the identification of arg-1, arg-2, and arg-3, three genes that each encode a different enzyme in the arginine biosynthetic pathway. Yeast is haploid, which means that all of the genes in yeast are "haploid insufficient" to carry out their jobs. Mutations that disrupt the activity of arg-1 or arg-2 or arg-3 result in yeast that cannot synthesize arginine. Imagine someone hands you two tubes of DNA, one has a wild-type copy of arg-2 and one has a wild-type copy of arg-3. To test whether these genes "work" you try rescue experiments as follows: (1) You add the wild type arg-2 gene to an arg-2 mutant strain. You reason that if the wild type arg-2 gene works, the strain should be able to live on minimal media. And it does! (2) You add the wild type arg-3 gene to the arg-3 mutant strain. You reason that if the wild type arg-3 works, the strain should be able to live on minimal media. But it doesn't! Oddly the DNA sequence of the wild-type arg-3 is 100% correct. Moreover, you find by RNAseq that the wild-type arg-3 gene is expressed in the yeast you added it to. Therefore, it seems it should have worked! Using molecular principles discussed in class, what kind of mutation (e.g. null, loss-of-function, dominant-negative, dominant gain-of-function) do you think best characterizes the arg-3 mutant allele? Name the type of mutation that best describes the arg-3 mutant allele and explain your reasoning in one sentence:Explanation / Answer
the type of mutation that best describes the arg-3 mutant allele has is a los of function mutation, where the RNA is expressed and the gene products are made but these products have less or no functions at all. when the allele has a complete loss of function, it's often called amorphic mutation.
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