Mutations Flashcards
Mutations
Changes in the base sequence of A GENE’S DNA that lead to formation of a new allele
How does a mutation lead to change in polypeptide?
Change in base sequence of gene’s DNA
Change in primary structure of polypeptide
Alters position of hydrogen bonds/ ionic bonds/ disulfide bridges
Change in tertiary structure of polypeptide
All types of mutation
Addition
deletion
substitution
inversion
duplication
translocation
Addition mutation
Addition of new base(s) to a gene’s DNA base sequence
Deletion mutation
Deletion of bases from a gene’s DNA base sequence
Substitution mutation
Switching one base for another in a gene’s DNA base sequence
Inversion mutation
Reversing base sequence of a gene’s DNA
Duplication mutation
Repeating of a base sequence in a gene’s DNA base sequence
Translocation mutation
A base sequence is moved from one locus on a DNA molecule to another DNA locus, on the same chromosome or on a different chromosome
When does translocation mutation usually occur?
During mistakes in crossing over in meiosis: mutated gametes more likely than body cells
Do mutations occur randomly?
Yes
Can you predict where mutations usually occur?
No
Effect of mutations on the organism can be….
Good
Bad
Neutral
Completely random which one
Spontaneous mutations
Happen most in naturally occurring processes eg DNA replication, meiosis
Randomly occur with no known cause
Mutagenic agents
Factors that increase the rate that random mutations can occur at
Where do gene mutations originate in?
DNA’s triplets of bases
Affects codons of bases on mRNA thus polypeptide’s amino acid sequence
Why do mutations in DNA matter more than in transcribed mRNA
Because this mutated DNA will transcribe mRNA and effect ALL polypeptides translated from this gene
And this mutated gene will be passed onto offspring
Degenerate
Most amino acids can be encoded for by more than one base triplet
Are substitution mutations likely to affect sequence of AA on polypeptide?
No because genetic code is degenerate so likely the substituted base that results in a new triplet will still encode for same amino acid: no change in primary structure: no change in H/ionic/disulfide bonds: no change in tertiary structure
Frameshift
Describes mutations that change the nature of base triplets downstream of the mutation
So change amino acid sequence in the polypeptide from the mutation
Examples of frameshift mutation
Addition
Deletion
How can a mutation have no effect on an individual?
Mutation occurred in intron/non coding sequence of DNA base sequence so will not affect translation (spliced out of mRNA)
Occurred in a recessive allele of this gene so not expressed in phenotype
Occurs at point in polypeptide that does not change tertiary structure
Substitution base = diff triplet that encodes for same AA
How can a mutation have a positive effect on an individual?
Changes polypeptide due to change in AA sequence that positively changes properties of protein
Which leads to increased survival chance and increased reproductive success
How can a mutation have a negative effect on an individual?
Changes polypeptide sequence due to change in AA sequence that negatively changes properties of protein
Leads to decreased survival chance and decreased reproductive success
Chromosome mutation
Changes in number or structure of chromosomesH
How do chromosome mutations differ from gene mutations/
Gene mutations occur within specific base sequence in a gene in a chromosome
Chromosome mutations occur during meiosis in the number of chromosomes in each cell
Example of chromosome mutation
Chromosome non disjunction
Chromosome non disjunction
Failure of homologous chromosomes/sister chromatids to separate properly during meiosis
So one gamete ends up with too many copies of the same chromosome
Non disjunction in meiosis 1 results
Homologous chromosomes don’t separate
So when sister chromatids separate in meiosis 2:
2 gametes produced that lack this chromosome
2 gametes produced that have double this chromosome as non sister chromatids both enter gamete (homologous) but sister chromatids have separated so we have 2
Non disjunction in meiosis 2 results
Homologous chromosomes separate as normal
meiosis 2 means no separation of sister chromatids in one of the daughter cells of meiosis 1
so 1 gamete has 2 copies of same chromosome and 1 gamete does not have this chromosome
What causes chromosome non disjunction?
Spindle fibre failure to separate sister chromatids or homologous chromosomes
