Mutations Flashcards
What is a mutation?
A heritable change to the DNA sequence of an organism
What is a wild-type allele?
The most prevalent allele in a population
What are 4 ways to classify mutations?
Where it came from, effects at a molecular level, effects on the phenotype, effects on gene product activity
Can mutations be spontaneous?
Yes, but they are rare because of proofreading mechanisms and repair find and fix most of them
What is a mutagen?
A substance that induces a mutation
What are the 3 classes of mutagens?
Chemical, physical, biological
What type of mutations are generated by chemical mutagens?
Point mutations
What are the 3 major mechanisms used by chemical mutagens to generate mutations?
Base modification, intercalating into the DNA backbone, base analogs
How does base modification create mutations?
Adding modifications to bases changes their H bonding properties, so they base pair with something else
What mechanism does EMS cause mutations through?
Base modification. Changes guanine to O-6-ethylguanine which base pairs with a T instead of C. Causes base pair substitutions
How does backbone intercalation create mutations?
Alters the physical structure of DNA and stalls replication, leading to the incorporation of incorrect bases
What mechanism do acridine and ethidium bromide cause mutations through?
Backbone intercalation. They are large, planar, multi-ringed molecules that in between the bases and disrupt the structure of DNA. Cause indels
How do base analogs create mutations?
They mimic normal bases and get incorporated during replication, but they base pair with the wrong thing
What mechanism does 5-bromouracil cause mutations through?
It mimics a thymine, so gets incorporated during DNA replication. The enol form will base pair with a G instead of an A
What types of mutations are generated by physical mutagens?
Large scale double strand breaks that result in deletions, inversions, or translocations. Pyrimidine dimers
What is ionizing radiation? What type of DNA damage and mutations does it cause?
Fast, high energy forms of radiation. Includes gamma rays, x-rays, fast neutrons. They create double strand breaks. Can result in deletions, inversions, or translocations
What is non-ionizing radiation? What type of DNA damage and mutations does it cause?
Lower energy radiation that doesn’t cause strand breaks, aka UV light. Causes pyrimidine dimers
What are the two types of deletions that could be caused by ionizing radiation? Which one is more common?
Terminal (end of the chromosome) and interstitial (inside a chromosome). Terminal is more common because it only requires one strand break
What type of mutations are caused by biological mutagens?
Insertions and deletions
What are transposons?
Moveable pieces of DNA that are endogenous to every eukaryotic genome
What is an advantage to using transposons?
Cloning the affected gene is very easy, since we know the sequences of the transposon and use restriction enzymes to figure out where in the genome the mutation occurred
How can transposons generate deletions?
If it is removed, it will take a bit of the surrounding DNA when it leaves and cause a small deletion
What are the two mechanisms by which transposons generate mutations?
Replicative transposition and non-replicative transposition
What is replicative transposition?
The original transposon gets copied, and the copy moves to a new location, but the original stays put and does not generate a deletion. Proceeds through an RNA intermediate (copy and paste)
What is non-replicative transposition?
The original transposon gets cut out from where it was and gets moved to another location. Creates a deletion where it originally was
