03/04 mutations Flashcards
what was Darwin’s idea of genetic variation
he believed that variation always existed within individuals but the selectional pressure of the environment is what selected certain traits as favorable
what was the idea behind use and disuse being the cause of genetic variation
they believed that the use of certain traits is what caused them to be passed down to offspring
what is the idea behind mutations that occur by pre-selectional force?
these mutations occurred without the influence of selection and happened before the force was applied. it just so happened that the selectional force favored the mutation
what is the idea behind mutations that occur by post-selectional force? is this idea correct?
this idea is not correct. the idea is that mutations occur with directionality and are caused by the selective force itself. the mutation occurs as a result of a selectional force.
in the lederberg replica plating experiment, what were the results
the random mutation occured by pre-selective forces and the same mutated bacteria was transferred to each of the plates
What if the physiological adaptation hypothesis was correct and you performed the lederberg replica experiment? what would you see on the plates
the mutation would not occur until the selective pressure was applied, when the bacteria were exposed to the T1 bacteriophage they begin to mutate as a means to survive, but the cells that will actually be successful will be random
the colonies would be randomly dispersed
how does the lederberg replica plating experiment support pre-selective forces and the random mutation theory?
the mutation occured before the selective pressure was applied. The cells that were going to survive the bacteriophage were already preselected for and this was not influenced by the presence of the bacteriophage
if the lamark theory of physiological adaption was true, what would the plates show in the lederberg experiment?
the mutation would occur after the selective force was applied, but it is unpredictable which cells will survive so the colonies that form will be random and non uniform
what is the idea behind the random mutation theory
it aligns with darwins idea of mutation already existing prior to selection. It suggests that mutations occur randomly without selectional pressure
what is the idea behind the physiological adaption theory
it suggests that the mutation occurs due to the selectional pressure
describe the random mutation theory in the context of the fluctuation test
it predicts that the number of mutated (torR) bacteria will fluctuate in differential bacterial populations based on the timing of mutations
why is it important that the number of bacteria fluctuated in the fluctuation test?
it tells us that the mutations occurred randomly throughout the replication cycles of the bacteria and some of the cells mutated earlier than others.
it also tells us that the mutation occured before the cells were plated (pre selection)
what was the experimental question in the fluctuation test by Luria and Max Delburk?
How often does mutation occur given the experimental parameters and how does the number of mutations fluctuate
in the fluctuation test, what was the idea of the physiological adaption theory
it predicted that the number of mutated bacteria will be in constant proportion or evenly distributed across the plates, indicating that all the bacterial cells mutated at the same time
if the physiological adaption theory was correct, what would the plates look like
they would look like the control in the experiment with an evenly distributed amount of bacterial colonies
what is a mutation rate
the likelihood that a gene will be altered by a mutation
is the rate of mutation constant
no, it can be increased by the presence of mutagens and some genes may have a higher rate of mutation
what is a hot spot?
it is a location in a chromosome or single gene that is more susceptible to mutation
what is a spontaneous mutation
it is a mutation that occurs naturally and cannot be avoided
what is an induced mutation
it is a mutation caused by outside factors that can be avoided
what is a mutagen
it is a chemical or physical mutation agent
what is the most common spontaneous mutation? why?
dupurination; it occurs due to a spontaneous reaction with water
what is depurination
it is the removal of a purine (adenine and guanine) from DNA due to a spontaneous reaction with water at the apurinic site
can apurinic sites be repaired? why does it matter how soon it is repaired?
yes they can, if they are not repaired before DNA replication, there is only a 1/4 chance of fixing the error and it is harder in subsequent rounds of replication
what is deamination
it is when a amino group is removed from pyrimidines (usually cytosine)
what happens if cytosine is deaminated in prokaryotes
it forms uracil
if a deaminated cytosine forms uracil and is not corrected by a repair enzyme, what might occur in DNA replication
the U may be paired with an A
in subsequent repair, the U may be replaced with a T instead of a C
why is 5-methyl cytosine a hot spot for mutation?
when 5-methyl cytosine is deaminated, it forms thymine which is a base commonly found in DNA.
In DNA replication, this thymine may be base paired with Adenine instead of guanine as intended
in what types of cells are there 5-methyl cytosines
eukaryotic
true or false?
deamination and depurination will result in insertion and deletion mutations
false, it is a substitution
true or false, deamination will cause a frameshift
false, only insertion and deletions will cause this
what are tautomeric shifts? why are they a problem
they are changes in conformation, they can result in incorrect bond formations
when in its common form, complementarity is followed in DNA replication. If it is in its rare tautomer form, what will occur?
rare bonds like AC and GT may form due to changes in the hydrogen bonding states
for a tautomeric shift to cause a mutation, when must it occur
right before DNA replication
if the rare tautomeric form of a nitrogenous base occurs but then returns back to its more common state before DNA polymerase converts it back into the new DNA, then it wont be a problem and cause a mutation
true or false
true
what was lamark’s theory of the cause of mutations?
he believed in the idea of physiological adaptions and how the environment can drive a mutation to occur when a selective pressure is applied
what is an example of a hot spot for mutation in eukaryotes
5-methyl cytosine, it is prone if deamination
what type of mutation is 5-methyl cytosine prone towards
deamination to form thymine
