Genetic Mutations Flashcards
What is a gene mutation
A change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide
How often do mutations occur
Continuously and spontaneously within a population
How can a mutation in a gene lead to a change in the polypeptide it codes for
The DNA base sequence determines the sequence of amino acids that make up a protein. Therefore, mutations in genes can occasionally change the polypeptide.
Why do most mutations not alter the polypeptide
The genetic code is degenerate
What does it mean if a genetic code is degenerate
Multiple codons can code for the same amino acid
What are the different ways that a mutation in the DNA base sequence can occur
Deletion, Insertion or Substitution
What is similar about insertion and deletion of nucleotides
Both change the amino acids that would have been coded for
What happens during a substitution mutation of nucleotides
A base in the DNA sequence is randomly swapped for a different base
What are the 3 forms of substitution mutation
Silent mutations, Missense mutations, Nonsense Mutations
What occurs during a silent substitution mutation
This mutation does not alter amino acid sequence of the polypeptide (this is because certain codons may code for the same amino acid as the genetic code is degenerate)
What occurs during a missense substitution mutation
Alters a single amino acid in the polypeptide chain
What occurs during a nonsense substitution mutation
Creates a premature stop codon (signal for the cell to stop translation of the mRNA molecule into an amino acid sequence) causing the polypeptide chain produced to be incomplete and therefore affecting the final protein structure and function
What is a deletion mutation
A mutation that occurs when a nucleotide (and therefore its base) is randomly deleted from the DNA sequence.
What generally happens after mutations
Most mutations do not alter the polypeptide or only alter it slightly so that its appearance or function is not changed
What type of mutations are insertion + deletion known as
Frameshift Mutations
What does a deletion mutation do further down the chain
Like an insertion mutation, deletion has a knock on effect by changing the codons further on in the DNA sequence
What do a small number of mutations do
code for a significantly altered polypeptide with a different shape
What can happen as a result of a mutation that codes for an altered polypeptide with a different shape
This may affect the ability of the protein to perform its function. E.g. If the shape of the active site on an enzyme changes, the substrate may no longer be able to bind to the active site
How do natural mechanisms within cells ensure the accuracy of DNA replication
By proofreading and repairing damaged DNA
How do you know when the natural mechanisms within cells that ensure the accuracy of DNA replication have become ineffective
When the mutation rate of a cell rises to above a normal (usually low) rate
What are mutagenic agents
environmental factors that increase the mutation rate of cells
Give examples of mutagenic agents
High-energy radiation such as UV light
Ionising radiation such as X rays
Toxic chemicals such as peroxides
What is non - disjunction and how does it occur
when chromosomes fail to separate during meiosis. This occurs spontaneously
Explain the outcomes for gametes of non - disjunction
The gametes may end up with one extra copy of a particular chromosome or no copies of a particular chromosome. Therefore, will have a different number of chromosomes to normal haploid number.
What happens if abnormal gametes (which suffered from non -disjunction) take part in fertilisation
A chromosome mutation occurs as the diploid cell will have the incorrect number of chromosomes. Chromosome mutations involve a change in the number of chromosomes.
Give an example of a chromosome mutation
Down’s syndrome: Individuals with this syndrome have a total of 47 chromosomes in their genome as they have three copies of chromosome 21
What occurs during an insertion mutation
A nucleotide (with a new base) is randomly inserted into the DNA sequence, changing the amino acid that would have been coded for by the original base triplet and having a knock on effect by changing the triplets further on in the DNA sequence.
What do all homologous chromosomes have in common
Every homologous pair contains the same genes at the same loci but they may contain different alleles for some or all of the genes.
What happens if there is more than one allele at a particular gene locus
There is more than one possible phenotype, resulting in genetic diversity
What are loci with more than two alleles known as
Polymorphic gene loci
What are the physical traits determined at loci with multiple alleles called
Multiple allele characteristics
What does having more than two alleles at a particular gene locus do
Increases genetic diversity
What do all organisms of the same species have in common
They all have similar genomes, though two individuals (even twins) will have differences between their DNA base sequences, but considering the size of genomes these differences are small
What is needed for natural selection to occur
some level of genetic diversity
