| What is a mutation | - Any change to the quantity or the base sequence of the DNA of an organism
- Mutations occurring during the formation of gametes may be inherited, makes sudden distinct differences between individuals
- Can arise spontaneously during DNA replication |
| What is a gene mutation | - Any change to the one or more nucleotide bases
- Or change in the sequence of bases in DNA
- A random change in the base sequence of DNA |
| Substitution of bases | - A nucleotide is replaced by a different nucleotide
e.g. ATgCCT becomes ATtCCT |
| Deletion of bases | - Removal of one or more nucleotides
e.g. ATgCCT becomes ATCCT |
| The affect of mutations | - The sequence of DNA bases in a gene determines the sequence of amino acids in a protein
- If mutation occurs in gene, changes sequence of amino acids so forms different polypeptide |
| The degenerate nature of the genetic code and substitution mutations | - Some amino acids are coded for more than 1 triplet
- So, not all substitution mutations will result in a change to the amino acid sequence of protein
- Some substitution will code for the same amino acid |
| Genetic code and deletion mutations | - Deletion will cause change in sequence of amino acids
- Deletion of a bases will change no. of bases, causing a frameshift in all the base triplets after it |
| How can a mutation lead to the production of a non-functional protein | - Mutation causes frame shift
- Changes amino acid sequence
- Affects bonds in tertiary
- Changes tertiary structure |
| Chromosome mutations | - Changes in whole sets of chromosomes
- Changes in the number of individual chromosomes, non-disjunction |
| Changes in whole sets of chromosomes | - Occur when organisms have 3 or more set of chromosomes rather than usual 2
- This condition called polyploidy, occurs mostly in plants |
| Changes in the number of individual chromosomes | - Sometimes individual homologous pairs fail to separate during meiosis
- This is called non-disjunction |
| Non-disjunction | - Usually results in a gamete having either 1 more or less chromosomes
e.g. Down syndrome, additional 21 chromosomes |
| What are mutagenic agents | - Cause in increase in the rate of mutations |
| Examples of mutagenic agents | - Carcinogen
- Ionising radiation
- UV |
