You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
Based on the number of sets of genes per cell, Neurospora is classified as
A. |
B. |
C. |
D. |
Neurospora is capable of undergoing asexual reproduction when its spores germinate. Is this statement true or false?
When Neurospora MAT-A and MAT-a cells come into contact, transient diploid nuclei form, which undergo meiosis. Is this statement true or false?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
How does nitrosoguanidine work as a mutagen?
A. |
B. |
C. |
D. |
Does the structure of nitrosoguanidine resemble the structure of any DNA bases or base pairs?
Guanine and cytosine base pair using three hydrogen bonds. If the oxygen in guanine were unavailable for hydrogen bonding, would that make a guanine-thymine base pair more likely?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
What is a prototroph?
A. |
B. |
C. |
D. |
What is the composition of minimal medium?
Which of the following organisms could be classified as prototrophic?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
What is an auxotroph?
A. |
B. |
C. |
D. |
Nutritional mutants of microorganisms can be isolated by replica plating between minimal medium and minimal medium supplemented with one or more essential biochemical building blocks. Is this statement true or false?
Prototrophs contain biochemical pathway mutations that are absent in corresponding auxotrophs. Is this statement true or false?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
The Neurospora nic-2 mutants are
A. |
B. |
C. |
D. |
Why is nicotinamide required in the medium in order for Neurospora nic-2 mutants to grow?
Recall from Steps 3 and 4 what distinguishes prototrophs from auxotrophs.
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
What is the significance of using a medium lacking nicotinamide?
A. |
B. |
C. |
D. |
What type of Neurospora will grow on this medium?
Plating cells onto medium lacking nicotinamide will select between cells that can synthesize nicotinamide and those that cannot. Is this statement true or false?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
How were the cells containing the two different nic-2 alleles obtained?
A. |
B. |
C. |
D. |
E. |
What is the purpose of inducing mutagenesis in this experiment?
What is the purpose of selection in this experiment?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
What does reversion mean?
A. |
B. |
C. |
D. |
E. |
F. |
Consider the general-purpose definition of the verb to revert.
The mutation under investigation is
The starting population of Neurospora were all nic+. Is this statement true or false?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
Which of the following mechanism(s) could cause a reversion in phenotype?
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B. |
C. |
D. |
E. |
F. |
G. |
If a mutation within a coding sequence of an A-T base pair to G-C is later converted back to A-T, would the coding sequence be restored?
If a base pair within a coding sequence is deleted, then a frameshift would occur in the transcript. If a different base pair is later inserted downstream of the deletion, could the original amino acid sequence be restored?
A mutation in gene X leads to loss of a protein X binding to protein Y, which blocks a biosynthetic pathway. Later a mutation in gene Y restores binding between proteins X and Y. Could this remove the block in the biosynthetic pathway?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
Why were no prototrophs detected when cells containing nic-2 allele 1 were mutagenized and plated onto selective medium?
A. |
B. |
C. |
Nitrosoguanidine always mutates specific nucleotides within DNA. Is this statement true or false?
The failure to include nicotinamide in the medium prevented the identification of prototrophs. Is this statement true or false?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
Why were no prototrophs detected when cells containing nic-2 allele 1 were mutagenized and plated onto selective medium?
A. |
B. |
C. |
D. |
E. |
F. |
G. |
Nitrosguanidine mutates DNA by
Nitrosoguanidine mutates nucleotides within DNA more or less randomly. Is this statement true or false?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
When a prototrophic revertant is crossed with wild-type Neurospora, how many progeny should typically come from wild-type ascospores?
A. |
B. |
C. |
D. |
Meiocytes are
During meiosis, one set of 2n meiocytes are converted to
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
A suppressor mutation that suppresses the effect(s) of the first mutation can restore the original wild-type phenotype. Is this statement true or false?
A. |
B. |
In this experiment what is the wild-type phenotype being followed?
Look up the definition of a suppressor in your textbook glossary.
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
When the progeny in a cross reveal a recombination frequency of less than 50%, then the genes being analyzed are linked. Is this statement true or false?
A. |
B. |
What is the relationship between recombination frequency and the distance between genes that are located on the same chromosome?
What does it mean when two genes are linked?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
When organisms containing nic-2 allele 2 were mutagenized and plated onto selective medium, three prototrophic colonies were isolated. What is/are likely molecular explanation(s) for why 100% of the progeny were prototrophic from the cross of prototroph A with wild-type Neurospora?
A. |
B. |
C. |
D. |
Fifty percent of the progeny from this cross came from wild-type ascospores. Is this statement true or false?
As you evaluate each answer choice, think like Mendel and consider that the outcome of a genetic cross has probabilistic underpinnings. Therefore, in order for 100% of the progeny to be prototrophic (that is, having reverted to wild type), what event is most likely to have happened?
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
When organisms containing nic-2 allele 2 were mutagenized and plated onto selective medium, three prototrophic colonies were isolated. What is/are likely molecular explanation(s) for why 78% of the progeny were prototrophic (and 22% were auxotrophic) from the cross of prototroph B with wild-type Neurospora?
A. |
B. |
C. |
D. |
The number of progeny, 78 prototrophs to 22 auxotrophs, approximates what well-known Mendelian ratio?
Prepare a Punnett square for two genes having two alleles of each gene in a haploid organism.
You are using nitrosoguanidine to "revert" mutant nic-2 (nicotinamide-requiring) alleles in Neurospora. You treat cells, plate them on a medium without nicotinamide, and look for prototrophic colonies. You obtain the following results from two mutant alleles.
a. With nic-2 allele 1, you obtain no prototrophs at all.
b. With nic-2 allele 2, you obtain three prototrophic colonies, A, B, and C, and you cross each separately with a wild-type strain of Neurospora. From the cross prototroph A × wild type, you obtain 100 progeny, all of which are prototrophic. From the cross prototroph B × wild type, you obtain 100 progeny, of which 78 are prototrophic and 22 are nicotinamide requiring. From the cross prototroph C × wild type, you obtain 1000 progeny, of which 996 are prototrophic and 4 are nicotinamide requiring.
Explain these results at the molecular level.
Unpack the Problem: Break this problem into several parts and arrive at a solution using this guided, step-by-step approach.
When organisms containing nic-2 allele 2 were mutagenized and plated onto selective medium, three prototrophic colonies were isolated. What is/are likely molecular explanation(s) for why 99.6% of the progeny were prototrophic from the cross of prototroph C with wild-type Neurospora?
A. |
B. |
C. |
D. |
In this cross of prototroph C and wild type, is it still true that 50% of the 1000 progeny come from wild-type ascospores?
Does the ratio of prototrophs to auxotrophs among the progeny correspond to a Mendelian ratio?
In this experiment, when the ratio among progeny phenotypes deviates significantly from what is expected, then what might the cause be?
Conclusion
Inducing mutations is a powerful tool that geneticists use for generating phenotypic variants. These variants can then be studied to identify the mutated genes as well as the gene products that the wild-type genes encode. These studies can be extended, in some cases, to unravel biochemical pathways or identify protein interactions. The creation of revertants can be used to identify additional genes (e.g., suppressors) and their gene products.