1.6 Mutation Flashcards
What is a mutation?
a mutation is an irreversible change in the genome resulting in no protein or a defective protein being produced
What is a mutant?
a change in genotype due to a mutation causes a change in phenotype of the organism which is referred to as a mutant
What is mutation the only source of?
genetic variation on which evolution depends on
What are mutagenic agents?
The frequency of mutations (how often they occur) may be increased by mutagenic agents such as gamma rays, ultraviolet light, chemicals in cigarette smoke and mustard gas
R O L F
Random
Occurence
Low
Frequency
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Random mutation of genetic material within a cell is a source of genetic variation forms the bases of the processes of natural selection, speciation and evolution
What are single gene mutations?
single gene mutations occur within genes and involve alterations of a DNA nucleotide/base sequence
Gene mutations result in no protein or an altered protein being produced
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Single gene mutations are a bit like spelling errors in the genetic code
What is insertion?
An additional base sequence into triplet of bases altering the base sequence of the gene from the point of the insertion
Many base triplets coding for many amino acids are affected causing a major change in the structure of the finished protein
this is a frameshift mutation
What is deletion?
a base is deleted from a triplet of bases altering the base sequence from the point of the deletion, as all triplets move along one space to fill the gap
Many base triplets coding for many amino acids are affected causing a major change in the structure of the finished protein
this is a frameshift mutation
What is substitution?
one base (nucleotide) within a triplet of DNA bases is substituted for another base, coding for one different amino acid in the polypeptide chain this causes a minor change to the finished protein
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Genes
Deletion
Insertion
substitution
What is a silent mutation?
a substituted nucleotide (base) results in a triplet that codes for the same amino acid and protein is normal
What is a neutral mutation?
a substituted nucleotide (base) results in a triplet that codes for a different amino acid that is similar to the original and the mutated protein still functions normally
What is a missense mutation?
A substituted nucleotide (base) results in a triplet that codes for a different amino acid which changes the function of the protein
what is a nonsense mutation?
a substituted nucleotide (base) results in a stop codon so the polypeptide chain is shorter
What is a splice site?
a mutation at a splice site may mean that some introns are not cut out of the primary mRNA transript
these introns will be read during translation and the protein will have extra amino acids which will after the structure and function of the protein
What is a nucleotide sequence repeat?
a repeat expansion mutation can increase the number of times a short sequence of three or four base pairs is repeated
this can affect the function of a protein that is coded for a gene
Example - Huntington’s disease (HD)
is caused by the expansion of a CAG DNA triplet repeat in a gene which codes for a protein protein whose absence can lead to the neurological degeneration linked to HD in humans
Regulatory Sequence Mutations?
Some regions on chromosomes are regulatory genes
They may code for small repressor proteins that block the expression of genes. Their advantage is that they stop the production of large proteins when they are not needed, saving energy and resources
They may code for activators proteins that promote the transcription of genes
Mutation in regulator genes can change the expression of genes resulting in absent or excess proteins, changing the phenotype of the organism
such mutations may be lethal
What is the significance of gene mutation in Evolution?
Point mutations are a source of variation
Occasionally the new form of the gene (allele) formed by the mutation can result can result in a protein that gives the organism a selective advantage
If this organism has a belter chance of surviving to reproduce the new alleles the new alleles will increase in frequency in the population
What is chromosome structure mutation?
Where whole sections of chromosomes containing many genes are broken, rearranged or lost
What is Deletion?
occurs when two breaks happen along the length of the chromosomes and the middle segment of chromosome with many genes is lost
What is Inversion?
Occurs when two breaks happen along the length of the chromosome, the segment of chromosome between the breaks rotates 180 degrees and reattaches, reversing the gene sequence
