MMG 301 Study Guide - Midterm Guide: Wild Type, Frameshift Mutation, Nonsense Mutation
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MMG 301 Exam 2 Info:
• Mutant: an organism with a heritable change in genome sequence that can be passed
down to its offspring
• Genotype: the nucleotide sequence (the entire bacterial genome as a genotype) (you
could consider a single gene as a genotype) a mutant will have a change in the
genotype
• Phenotype: all the observable properties of an organism (ex: what it can grow on, what
does it use for energy, nutritional requirements, does it produce a toxin, is it resistant to
antibiotics)
• A wild-type: is a strain of organism as isolated from nature (presumably does not have
any mutations). (think of it as the control or reference) (sort of the default phenotypes
and genotypes you are looking at)
• A mutation is a change in a genome base sequence compared to the wild-type
sequence.
• In the case of bacteria, when the bacteria divide into two, the mutation goes to both
• So genotypes resulting in change in phenotypes, so that is generally how you would find
a mutant
• Only way to know if there has been a change is to have your control at the beginning
•
• Dna -> transcription -> Rna -> translation -> protein
• -DNA defines your genotype
• protein are what produces the phenotypes (for the most part, but RNA can contribute
to this as well given that RNA can act as an enzyme)
• when you have a mutation, you will have a change in the genotype, that change will be
probably propagated through to the RNA, and then potentially, definitely maybe, to the
phenotype
• A mutation is a change in a genome base sequence compared to the wild-type
sequence.
o Spontaneous mutations occur naturally without human intervention.
o Induced mutations result from intentional exposure to chemical agents or
radiation (mutation agent aka DNA alkylating agents)
• spontaneous mutations occur bc DNA polymerase, which is responsible for replicating
the genome, it makes an error somewhere around one times 10 to the minus nine base
pairs, so basically every 1 in a billion pairs, it will make a mistake (1 x 10^-9 base pairs
aka bp) so you get spontaneous mutations about that often
• in induced mutations, when you add these chemicals or radiation, you just tend to
increase the frequency of this (so this ups the frequency of that other number) which
can occasionally make things a lot easier to isolate if what you’re looking for is a rare
event
•
• -grow your wild type cells (first green dish) on a master plate, and this is a growth
medium that is complete
• -there is a spontaneous mutation rate, so there will be changes that occur throughout
• -so some of these cells will be mutants
• -so lets say we are interested in isolating genes, that are involved with tryptophan
biosynthesis, so we want to find things that are trp biosynthesis, so what are the genes
that are involved in making the amino acid tryptophan?
• -one thing we may assume is that if we made a mutation in a gene involved in
tryptophan biosynthesis, the cells would require tryptophan to grow
• -so this media actually has tryptophan, plus trp, so we can take colonies from this media
and then plate them onto two different media, keeping the spatial orientation together,
and what we do when we have that is we can have a complete medium, so this is plus
tryptophan, and then we can also have a selective medium, so this is minus tryptophan
• -so the prediction would be in tryptophan biosynthesis genes would grow on these
plates after we incubate them but would not grow on these plates
• -then we can go back and start looking for these mutations
• -the reason we do this, for evolutionary purposes that these mutants exist on this place,
right. The mutants are already there. They are not introduced because we put them
onto a medium with no tryptophan, right, they just happened to occur and we are
managing to create a selection for them
• -this is very powerful, we can use this to figure out things like nutritional oxytrophies
like this or any other number of biosynthetic genes, resistance to antibiotics, etc
•
• Point mutations are changes to a single base pair