- What does a gene mutation involve?
A change in the base sequence of DNA.
- When can gene mutations occur?
They can arise spontaneously during DNA replication.
- Describe the result of a base deletion.
When a base is removed from a DNA nucleotide sequence, a frame shift occurs. This changes all of the triplet codes after the mutation, as well as the one where the base has been removed.
- Describe the result of a base substitution.
When a base is substituted for another, the code will only be changed for that triplet code, no others will be affected. It may mean that there is no change in the polypeptide coded for, due to the degenerate nature of the genetic code. Or the polypeptide coded for may change by that one amino acid. In extreme cases the polypeptide may be truncated due to the presence of a new ‘stop’ triplet code.
- What can increase the rate of gene mutation?
Mutagenic agents such as ionising radiation or carcinogenic chemicals.
- When can chromosome mutations occur?
Chromosome mutations can arise spontaneously by chromosome non-disjunction during meiosis.
- What are chromosome mutations?
Chromosome mutations include: changes in the whole set of chromosome, such as polyploidy. Or changes in the number of individual chromosomes, when chromosomes fail to separate during meiosis.
- What is non-disjunction?
When individual homologous pairs of chromosomes fail to separate during meiosis, so there will be more than 2 chromosomes in a homologous pair in the offspring.
- Explain how a mutation can result in a non-functional protein.
(Or a non-functional enzyme)
A change in nucleotide sequence gene; causes a change in amino acid sequence or primary structure of the protein; Change in hydrogen / ionic / disulfide bonds; Change in the tertiary structure;
IF enzyme:
Change in active site; Substrate not complementary so no enzyme-substrate complexes form.
