Gene Interruption Flashcards
Describe a metabolic pathway
Multistep process that either synthesizes (ex. amino acids, sugars) or degrades a complex molecule (ex. cellular respiration breaks down sugars)
What is an anabolic pathway?
A metabolic pathway that synthesizes complex molecules with the sequential action of genes and enzyme catalysts
What is a catabolic pathway?
A metabolic pathway that breaks down complex molecules through the sequential action of genes and enzymes as catalysts
Describe how metabolic pathways work
Genes work together in sequential order to produce a final product
if all the genes in a pathway are functional, they will produce enzymes to convert a compound to another compound in a step process
ex. Met 2 codes for enzyme homoserine transacetylase to convert homoserine to cysteine
then Met B codes for cystothionine gamma synthetase to convert cysteine to cystathionine… etc.
What happens if a gene in the pathway is not functional?
the gene will not be able to code for the enzyme that will convert the current compound to the next compound
What is Neurospora?
A haploid fungus
Model organism
Why is Neurospora a model organism?
It is a simple organism that is easy to study
mates quickly
mycelium is multinucleate (haploid)
if two different fungi have different mating types and come into contact, they can fuse to create a diploid cell that will undergo meiosis to recombine and produce new haploid offspring
they synthesize everything they need to grow
Describe prototroph
An organism that has the wild type phenotype and no mutations and can grow on minimal plating (has everything it needs)
Describe auxotroph
An organism that has a mutation in a gene required to synthesize an essential molecule
cannot grow on minimal medium
What does minimal medium usually contain?
minerals, water, a carbon source (glucose usually)
How are the genes involved in the synthesis of a particular amino acid studied?
Geneticists screen for mutants by looking for auxotrophs
What kind of medium will an auxotroph be able to grow on?
Minimal medium + the essential molecule they cannot produce
How do geneticists screen for mutants?
take prototrophic neurospora and radiate with mutagens (ex. X ray) to create mutations
plate these on complete medium to allow both prototrophs and auxotrophs to grow
transfer to minimal medium to determine which are auxotrophs (will not grow)
auxotrophs transferred to minimal media + different amino acids to identify the pathway
mutant strains that required methionine to grow are methionine auxotrophs
Describe a complementation test
a test to cross mutants to determine the number of genes involved in the mutation
What happens if you give a mutant a compound that is made in the metabolic pathway after the step where the pathway is blocked?
the mutant can make the end product
What happens if you give a mutant a compound that is made in the metabolic pathway before the step where the pathway is blocked?
The mutant will not be able to make the product
What are the steps of identifying genes involved in determining petal colours in peas (for example)?
expose plants to mutagens to create mutations
look at offspring to identify and isolate mutants in gene for petal colour = peas with non-wild type phenotype
T or F: many phenotypes are controlled by more than one gene
true
How do you identify if the mutation occurs in the same gene or in different genes?
- complementation test
2. analyze double mutants
how do you get the double mutants?
by crossing mutants from the complementation test
How do you conduct a complementation test for a diploid organism
Cross 2 homozygous mutant lines to produce heterozygote F1
How do the genes interfere if the F1 of a complementation test is heterozygous wild-type? Why?
The parents are mutants in different genes because both mutations were required to produce the wild-type phenotype
How do the genes interfere if the F1 of a complementation test is heterozygous mutant? Why?
Parents are mutant in the same gene because two copies of the mutant allele were required to show the mutant type
How can we tell if the two genes causing a mutation are interacting or acting independently?
by examining the phenotype of the double mutant organism
What is a double mutant?
An organism that is homozygous for the recessive/mutant gene
Created from complementation test F1
What is the phenotypic ratio for genes that do not interact?
regular dihybrid
9:3:3:1
What are 3 important phenotypic ratios for when genes do interact with each other?
9: 3:4
9: 7
12: 3:1
Which ratio will you see if there is complementary gene interaction?
9:7
Describe complementary gene interaction
the genes in a biochemical pathway act in tandem to produce a phenotype
Wild type action from both genes is required to produce the WT phenotype
mutations of one or both genes produces a mutant phenotype
In complementary gene interaction, how is the wild type phenotype produced?
When both genes are functioning for the wild type
In complementary gene interaction, how is the mutant phenotype produced?
When either of the genes have mutations
What is the ratio for recessive epistasis?
9:3:4
Describe recessive epistasis
the recessive allele of one gene masks or reduces the expression of alleles of a second gene
the mutation of one gene blocks the biochemical pathway and the mutant phenotype is produced
What is the phenotypic ratio of dominant epistasis?
12:3:1
Describe dominant epistasis?
when a dominant allele (functioning) of one gene masks or reduces expression of alleles of a second gene
What are 2 reasons that organisms can have the same genotype but not the same phenotype?
Sex-limited inheritance
sex-influenced inheritance
Describe sex-limited inheritance
These genes are located on autosomes in male and females, but the phenotype is only expressed in one sex
Why is the phenotype of a sex-limited gene only expressed in one sex?
differences in concentrations of sex hormones
Give an example of sex-limited inheritance
genes that affect sperm production will only show phenotype in male sex
genes that affect milk production will only show phenotype in organisms with mammary glands
T or F: sex-limited inherited genes can be passed on to offspring even if the parent did not express the phenotype
true
Describe sex-influenced inheritance
genes located on autosomes so both male and females receive
expression of phenotype affected by concentration of
Define complete dominance
one copy of the dominant allele produces enough functional protein to carry out normal cellular function
How does the phenotype of a homozygous dominant compare to a heterozygote when there’s complete dominance
the phenotypes are the same
Define haplosufficient
when a gene only requires one copy to express the normal function
T or F: wild type alleles are haplosufficient in complete dominance
True
Are mutations of haplosufficient genes dominant or recessive?
recessive
Explain complete dominance when the wild-type allele is recessive
one copy of the wild type allele does not produce enough functional protein to allow normal cellular function
Define haploinsufficient
when a gene requires more than one working copy to function properly
Mutations of haploinsufficient genes are recessive or dominant?
dominant
How does the phenotype of a heterozygote compare to homozygotes when a gene has incomplete dominance?
the heterozygote phenotype is an intermediate of two extreme homozygotes
What is the phenotypic ratio of the F2 generation when there’s incomplete dominance?
1:2:1
Which allele is dominant and which is recessive during incomplete dominance?
neither allele is dominant or recessive
