Mutations Flashcards
Mutations
in genes are random and their occurrence is rare
Mutation rate
Mutations per unit time
What are the 2 way mutation rate is measured?
at the phenotypic level, by counting the number of mutations affecting a phenotype; and at the molecular level, by deter- mining the frequency of mutations per base pair.
Measured at the phenotypic level
Number of mutations affecting a phenotype
~10-6 to 10-8 per gene
Measured at the molecular level
Frequency of mutations per base pair( certain base pairs within genes have higher mutation rates than others)
Things mutate at different rates according to where in the genome it is and the environmental factors affecting it
~10-9 per replicated base pair
Everyone in their cells have multiple mutation rates depending on the genes involved and specific cell types
mutation hotspots
Some genes mutate more than others
Larger genes mutate more than smaller genes because they have more nucleotides contained in their gene region
Ex. Human X-linked dystrophin (DYS) mutates at ~10-4
Germ-line mutations
Mutations are passed from one generation to the next
i.e. mutations that occur in genes and passed down via gametes
Mendel’s experiments with traits in peas are germ-line mutations
In sex cells and stem cells
This how we get phenotypes to change within population
Somatic mutations
Can be passed to future generations of cells in a cell lineage due to mitosis
BUT not passed to passed to further generations
Only direct descendants of the cells carrying the gene mutation
Only occurs in individual and cannot be passed down because it doesn’t occur in sex cell
Surrounding cells that result due to mitosis will get the mutation
Ex- cancer, cant be passed on to child
Point mutations
Confined to a specific base pair or gene location (changing one nucleotide to another nucleotide)
Add, delete, or substitute one or more base pairs
Can occur anywhere in the genome
Several kinds of point mutations
what is point mutations occurring in the coding sequence of a gene (in exons)
Could change the amino acid sequence- we will have different protein that has reduced different or no function
what happens if point mutation is occurring in the regulatory sequence of a gene (enhancers, repressors, etc.)
Could change the amount of gene expressed (ie less or more protein product) doesn’t change structure of protein
How do we describe coding sequence mutations?
based on “levels”
Amino acid level
RNA level
DNA level
Which mutations occur at the amino acid level?
is an amino acid change in the sequence? What was the effect?
Synonymous(amino acid stayed the same a mutation occurred but the leucine is still a leucine), nonsynonymous (amino acid changes)
We usually use these to describe the change/effect in the amino acid sequence
Which mutations occur at the RNA level?
did a nucleotide change that resulted in an amino acid change? (how did the codon change)
Missense(causes the amino acid to change), silent(codon will still code for the same amino acid but nucleotide changed),
nonsense(takes a codon that was coding for a amino acid and now codes for a stop codon, premature stoppage of polypeptide chain ),
nonstop(normally had a stop codon but it mutated and we no longer have the stop codon)
We usually use these to describe the change/effect in the codon
Which mutations occur at the DNA level?
How did the nucleotide change?(looking at the A G C T u)
Substitutions (transition, transversion), insertion/deletions (frameshifts)
We usually use these to describe the change in the nucleotides
*NOTE: All of these are a result of a change in the nucleotide sequence , which could affect the amino acid sequence