Podcast
Questions and Answers
What must be true concerning the location of the mutations for true complementation to occur?
What must be true concerning the location of the mutations for true complementation to occur?
- The mutations must be in different genes. (correct)
- The mutations must be heterozygous dominant.
- The mutations must be on sex chromosomes.
- The mutations must be in the same gene.
In complementation testing, what phenotypic outcome would suggest that two mutations reside within the same gene?
In complementation testing, what phenotypic outcome would suggest that two mutations reside within the same gene?
- The offspring exhibit an intermediate phenotype.
- The offspring exhibit a novel phenotype.
- The offspring exhibit a mutant phenotype. (correct)
- The offspring exhibit a wild-type phenotype.
Why is it important that mutations be homozygous recessive for true complementation to occur?
Why is it important that mutations be homozygous recessive for true complementation to occur?
- To prevent the dominant allele from masking the recessive allele.
- To ensure the mutant phenotype is expressed in the absence of complementation. (correct)
- To ensure the wild-type allele is expressed.
- To allow for the expression of both alleles.
How does complementation relate to the restoration of a wild-type phenotype in an organism with two mutant parents?
How does complementation relate to the restoration of a wild-type phenotype in an organism with two mutant parents?
What is the main function of the lac operon?
What is the main function of the lac operon?
What defines an operon?
What defines an operon?
How does the presence of lactose affect the lac operon?
How does the presence of lactose affect the lac operon?
What is the role of the regulatory gene (lacI) in the lac operon?
What is the role of the regulatory gene (lacI) in the lac operon?
What is the effect of a mutation in the operator region (Oᶜ) that prevents the repressor from binding?
What is the effect of a mutation in the operator region (Oᶜ) that prevents the repressor from binding?
In a lacIË¢ mutant, the repressor protein cannot bind to the inducer. What is the effect on the lac operon?
In a lacIË¢ mutant, the repressor protein cannot bind to the inducer. What is the effect on the lac operon?
If a bacterium has a mutation in the lacZ gene, preventing the production of β-galactosidase, what substrate can it no longer metabolize?
If a bacterium has a mutation in the lacZ gene, preventing the production of β-galactosidase, what substrate can it no longer metabolize?
What is the role of permease, encoded by the lacY gene, in lactose metabolism?
What is the role of permease, encoded by the lacY gene, in lactose metabolism?
How does IPTG facilitate blue-white screening?
How does IPTG facilitate blue-white screening?
What is the function of the lacA gene product (transacetylase) in the lac operon?
What is the function of the lacA gene product (transacetylase) in the lac operon?
In the absence of lactose, what prevents transcription of the lac operon?
In the absence of lactose, what prevents transcription of the lac operon?
What term describes an organism with a phenotype that is considered 'normal' for a particular trait?
What term describes an organism with a phenotype that is considered 'normal' for a particular trait?
What indicates a mutant allele next to the gene name?
What indicates a mutant allele next to the gene name?
What is the effect of the presence of both glucose and lactose on the lac operon?
What is the effect of the presence of both glucose and lactose on the lac operon?
What occurs when X-gal is cleaved by beta-galactosidase?
What occurs when X-gal is cleaved by beta-galactosidase?
What term best describes IPTG?
What term best describes IPTG?
Flashcards
Wildtype
Wildtype
The 'normal' phenotype for a particular gene, commonly found in a natural population, indicated by a '+' symbol.
Mutant
Mutant
A phenotype that differs from wildtype, indicated by a '-' symbol.
Complementation
Complementation
The act of masking a mutated gene with a functional gene to restore the wildtype phenotype.
Complementation Rule
Complementation Rule
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Operon
Operon
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Lac Operon
Lac Operon
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Lac Z-
Lac Z-
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Lac I^s
Lac I^s
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Lac I-
Lac I-
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Lac O^c
Lac O^c
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β-galactosidase
β-galactosidase
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Permease
Permease
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Transacetylase
Transacetylase
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Regulatory protein
Regulatory protein
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X-Gal
X-Gal
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IPTG
IPTG
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Study Notes
- Wildtype refers to an individual with a "normal" phenotype, which is a physical characteristic for a particular gene
- This phenotype is generally found in a natural population and is indicated by a "+" next to the gene name
- Mutant refers to an individual with a phenotype that's different from wildtype and is indicated by a "-" next to the gene name
- Sometimes organisms have mutations in two different genes that produces the same physical result. For example, white eye color in flies
Complementation
- Involves masking a mutated gene with a functional one to restore the wildtype phenotype
- Requires mutations to be in different genes, mutations must be homozygous recessive
- Crossing two mutant organisms to restore the "normal" phenotype
- Tests that can determine whether various mutations are on the same or different genes
- The mutations must be in different genes for true complementation to occur.
Operons
- A group of genes that function as a single transcriptional unit
- Expression of these genes is co-regulated and they are either all turned "off" or "on" at the same time
Lac Operon
- A group of genes involved in lactose metabolism in bacteria
- Bacteria can use lactose as an energy source
- There is efficient control of genes involved in processing
- Negative inducible, so normally off
Lac Operon Structure and Function
- Consists of a promoter region, 3 structural genes (lac z, y, and a), and the lac i gene
- Lac z encodes β-galactosidase
- Functions to degrade β-galactosides like lactose
- Lac y encodes permease
- Functions to transport β-galactosides into the cell
- Lac a encodes transacetylase
- Transfers acetyl group to allolactose,
- The function of lac a in operon is not well understood, but it may neutralize toxic byproducts
- Lac i encodes regulatory protein (repressor)
- Functions to prevent transcription of the structural genes
Mutations in the Lac Operon
- Lac z- cannot metabolize lactose
- Lac Is has a mutation in repressor that does not allow inducer to bind, so the operon is always off
- Lac I- has a mutation in repressor that prevents it from binding to the operator, so the operon is always on
- Lac O^c has a mutation in the operator that prevents repressor from binding to it, so the operon is always on
X-Gal and IPTG
- X-Gal identifies cells with beta-galactosidase activity
- When X-gal is cleaved, a blue green pigment is produced
- IPTG is an analog for allolactose
- Functions as an inducer for de-repression of the operon
- Blue white screening is when you can tell if Beta-galactosidase is present through color changes
- Screening vs selection
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