Metabolites in a biochemical pathway Here is a metabolic pathway in which precur

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Metabolites in a biochemical pathway

Here is a metabolic pathway in which precursor A is converted into the final product D. The sequence of steps in this process is as follows:

Each of the enzymes shown is the product of a different gene.

Part A

Which of the metabolite(s) would be missing in cells that are mutant for enzyme 2?

Select all that apply.

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Order of a biochemical pathway

You isolate a number of auxotrophic single-gene mutants (1, 2, 3, and 4) of Neurospora. These mutant strains can grow (+) when certain nutritional supplements (A, B, C, D, and/or E) are added to minimul culture medium. The table below shows the growth patterns for your mutant Neurospora strains according to the supplements provided:

No growth is indicated by a "0".

Part A

Take a look at the results for mutant strain 3. According to the table, this strain will be able grow in the presence of which supplements?

Select all that apply.

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Flower pigment

You identfy a new species of flower growing on top of Mt.. Its petals are normally purple (i.e., a mix of blue and red pigment). You are able to isolate two recessive mutations in separate plants. Mutation A (mA) results in blue petals when homozygous (mAmA). Mutation B (mB) results in red petals when homozygous (mBmB). You are able to figure out that the biochemical pathway for the synthesis of flower pigment in this species is the following:

Part A

What flower color would you expect in the mutant strain defective for enzyme 1?

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Part B

Which mutant strain is deficient in enzyme 1 activity?

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Part C

However, even the one-gene-one-polypeptide hypothesis is not entirely accurate.

Select all the reasons why.

Expression of one gene can result in more than one type of polypeptide

Separate mutations?

You obtain two independently-isolated auxotrophs of Neurospora, both of which are unable to synthesize the amino acid valine. In order to determine whether the mutations in these two auxotrophs are on the same gene, you could conduct a _________________ test.

Complementation with dominant mutations?

Part A

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mutant

Complementation tests can be used to determine whether two independently-isolated mutants with the same phenotype have mutations within the same gene. If mutations are on different genes, then complementation analysis will NOT restore the wildtype phenotype. In other words, the two mutants do not complement each other.

Complementation analysis can be used only to determine whether two the same gene mutations affect the same function. It cannot be used to determine whether two dominant alleles affect the same function. A dominant mutation will always show the recessive phenotype in a heterozygote. Because complementation tests with a dominant mutant can never produce a wildtype phenotype, results from such tests cannot be interpreted.

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Part I

The ratio you entered in Part H should immediately suggest to you that the phenomenon of ________ is present, i.e., that the alleles of these genes are interacting in the control of a single phenotype.

Explanation / Answer

Answer:

(1). The metabolites C and D would be missing in cells that are mutants for enzyme 2.

(2). The mutant strain 3 will be able grow in the presence of the supplements A, B, C and D.

(3). Part A: red color flowers would expect in the mutant strain defective for enzyme 1.

      Part B: Mutation B would be produced when the strain is deficient in enzyme 1 activity.

(4). Part C: Transcription of some genes does not result in a polypeptide, even the one-gene-one-polypeptide hypothesis is not entirely correct.

(5). You obtain two independently-isolated auxotroph’s of Neurospora, both of which are unable to synthesize the amino acid valine. In order to determine whether the mutations in this two auxotroph’s are on the same gene, you could conduct a Complementation tests.

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