Kolhalmi for Midterm Flashcards
Give 2 examples where a change in phenotype is NOT the result of a mutation
hydrangeas- flower colour depends on the soil pH
Himalayan bunny- have a colour-sensitive allele that turns black when cold
What are 3 characteristics that are often used to distinguish a WT allele?
considered to be the norm
more frequent
came first
What is important to remember when looking at the effects of mutations?
The effect of a mutation can depend on the conditions under which you observe it
What happens to the sequence on the top strand if there is an inversion?
it is now the 3’ sequence of the bottom strand backwards (i.e. 3’ to 5’)
Name 7 types of spontaneous mutations
depurination deamination X-rays breaking of the backbone pyrimidine dimers mistakes during replication un-equal crossovers slippage/unstable trinucleotide repeats
How often does DNA polymerase make mistakes? How does it correct some of these mistakes?
makes a mistake every 10^6 bp
has proofreading 3’ to 5’ exonuclease activity which fixes a lot of these errors
Where does slippage occur? When does it cause insertion? When does it cause deletion?
Occurs during runs or repeats
Causes insertion if the new strand slips
Causes deletion if the template strand slips
Name 2 diseases caused by slippage in trinucleotide repeats
Huntington’s disease
Fragile X syndrom
Name 5 times of induced mutations (mutagen alters DNA)
Base analogs Altering a base structure/property (add hydroxyl or methyl, remove amino) Intercalating agents Radiation (X-ray, UV) Biological agents (transposons, viruses)
What are endogenous mutations? What are 3 things that can cause them?
Mutations that occur from the inside Caused by: Nucleotide imbalances Metabolic processes going wrong Repair mechanisms going wrong
What cause exogenous mutations?
Any chemical that when applied causes changes in DNA
What is a toxin? What is a mutagen?
toxins kill you
mutagens change DNA
How often do you get a mutation when repairing an apurinic site?
3/4 of the time
What is unequal crossing over?
when 2 closely related DNA sequences that are located in two different places on homologous chromosomes recombine during meiosis
Describe Fragile X syndrome
Expansions of CGG triplets
premutation alleles have 50-200 repeats
disease causing have more than 200
What does alkyltransferase do?
remove mistakenly added methyl and ethyl groups from DNA
What does photolyase do?
Repairs thyamine dimers, needs light to function “photo repair”
Describe base excision repair
Take out an altered base creating an apurinic or apyrimidal site
Nick the backbone and take out a few nucleotides leaving a gap
DNA polymerase and ligase come in and fix it
Describe nucleotide excision repair
Cut in 2 places flanking DNA damage and take out then repair
Describe methyl-directed mismatch repair
Bacteria methylate adeneines on the parent strand so that they can recognize which member of a mismatched pair is the right one
What kind of repair systems use error-prone DNA polymerases?
SOS repair systems
What is a missense mutation?
amino acid changes
What is a null allele? Amorphic?
Null alleles means no protein is produced
Amorphic is a specific type of null allele where the protein is too deformed to function
If you are heterozygous for a null or amorphic allele what is your phenotype?
Still WT because you have enough WT protein to function
What is an example of a null allele?
Agamous Arabidopsis thaliana
What is a hypomorphic allele? What is the heterozygous phenotype?
Hypomorphic means reduced WT protein synthesis or that the produced protein has a weak function
Heterozygous phenotype is still WT
Explain the null and hypomorphic alleles in the eyeless gene in Drosophilia. What genes have similar function in humans? Mice?
null allele has no eyes
hypomorphic has small eyes
Mice have pax6 gene
Humans have aniridia gene
Does a null allele always mean that the structure i.e. legs are not produced?
No it just means the null version of this allele, there could be more than one gene involved in making the structure
Describe the null and hypomorphic alleles for a particular gene involved in Drosophilia leg and wing development
Hypomorphic give reduced wings and normal legs
Null gives reduced wings and legs
What is an example of incomplete dominance alleles?
colour of snapdragon flowers
r0 is null, produces no pigment
r50 loss of function, 50% of normal pigment
R is full red pigment produced
What is haplo-insufficiency?
one WT allele is not sufficient for a WT phenotype
this is a property of the WT allele NOT the mutant allele
What do mutants that are dominant loss of function mutations reveal?
dosage-sensitive genes
haplo-insufficient alleles
Give an example of a dominant loss of function allele?
T locus in mice for tails
heterozygotes have a short tail because one WT allele isn’t enough for a WT phenotype
If an organism is heterozygous for a dominant loss of function allele what is the phenotype?
mutant phenotype because it is haply-insufficient
What are antimorphic alleles?
dominant negative loss of function alleles
they block or interfere with the WT allele function
Give an example of a dominant negative loss of function allele? (antimorphic)
transcription factor homeodimer example
if you’re heterozygous you only have 1/3 functional protein and therefore have a mutant phenotype
What is a hypermorphic allele? What phenotype do heterozygotes usually have?
Increased protein synthesis or a protein with higher activity (WT amount of higher activity protein)
Heterozygotes have mutant phenotype
Give an example of a hypermorphic allele
Possum allele in mice
Heterozygotes have behavioural changes, they can’t turn over when on their backs and they get whole body immobilization when the scruff of their neck is pinched
What is a neomorphic allele?
When a mutation causes an allele to have a new function i.e. change what an enzyme does
What is ectopic expression?
Special type of neomorphic allele which results in a protein being expressed somewhere in normally isn’t
Give an example of ectopic expression
Antennapedia gene in Drosophilia
legs expressed out of the head
What can you adjust in a restriction digest to get what you want?
the time
how much enzyme
how long the recognition sequence is
What is a smear in reference to gel electrophoresis?
when your gel has so many fragments that you don’t see distinct bands just a smear along the whole lane
How would you make a restriction map?
Do 3 restriction digests with 2 different enzymes, once each and one with both
What 3 things does a vector usually have?
origin of replication
selectable marker
multiple restriction sites
How long are the primers usually used in PCR?
18-25 nucleotides
