Mutations & Meiosis Flashcards
Define gene mutation
Any change to one or more nucleotide bases or any rearrangement of the bases in DNA
How can gene mutations arise
They can arise spontaneously during DNA replication
Why is mutation important
It produces genetic diversity (resulting in speciation and natural selection)
Could produce an organism that is less/better suited to its environment
How are mutations passed on? What is not passed on
Through gametes (mutations in the gametes)
Mutations in normal body cells are NOT passed on
What are the 3 ways in which DNA base sequences occur
Substitution
Deletion
Insertion
What are the types of substitution
Silent
Nonsense
Missense
What is a mutagenic agent? Give examples
A factor that increases the rate of gene mutation, eg ultraviolet light or alpha particles
What is a silent mutation
A substituted base is different, but still codes for the same amino acid as it is degenerate. There is no change in the polypeptide
What is a nonsense mutation
When a base change results in a stop codon. The production of a polypeptide would be stopped prematurely, so the protein would be different and not function
What is a missense mutation
When a base change results in a different amino acid being coded for. This could result in a slightly different polypeptide. The effect of the mutation would depend on the role of the amino acid
What is a deletion mutation
When a nucleotide is lost from the normal DNA sequence
What is a insertion mutation
When another nucleotide is added
What is a frame shift caused by
A deletion or insertion mutation
How does a frame shift affect the group of codons of the reading frame
A triplet code can be changed so that every subsequent codon changes, so every amino acid sequence is different
Explain how a mutation can lead to the production of a non functional protein or enzyme
Mutations change the sequence of base triplets of DNA in a gene, so therefore changes the sequence of codons on mRNA
This means the sequence of amino acids in the polypeptide is changed
This changes the position of ionic/hydrogen/disulphide bonds between the amino acids, therefore changing the proteins tertiary structure
The enzymes active site changes as the tertiary structure changes, so the substrate cannot bind and the enzyme-substrate complex can’t form
Explain the possible effects of a substitution mutation
The DNA base is replaced by a different base, this changes one triplet so also changes one mRNA codon.
So either:
- One amino acid in the polypeptide changes and the tertiary structure changes if the position of the hydrogen/ionic/disulphide bonds change
OR
- The amino acid doesn’t change due to the degenerate nature of genetic code, or if the mutation is an intron and is removed during splicing
Explain the possible effects of a deletion mutation
One nucleotide is removed from the DNA sequence which changes the sequence of DNA triplets from the point of mutation (this is called a frameshift). This causes a change of sequence of mRNA codons after the point of mutation, which therefore changes the sequence of amino acids in the primary structure of the polypeptide. This later changes the position of hydrogen/ionic/disulphide bonds, which means the tertiary structure of the protein changes
What are a homologous chromosomes
Chromosomes that are the same length, have the same genes at the same loci, but have different alleles
Define diploid. What is it represented as?
Diploid cells have 2 complete sets of chromosomes
Represented as 2n
Define haploid. What is it represented as?
Haploid cells have a single set of unpaired chromosomes
Represented as n
Define the outcome of mitosis
Produces 2 daughter cells which are genetically identical
Define the outcome of meiosis
Produces 4 genetically different daughter cells with half the number of chromosomes
Why is meiosis important
Because it maintains a constant number of chromosomes in a cell after fertilisation and it creates variation
What is the purpose of meiosis 1
To separate pairs of homologous chromosomes
