3.4.3 Genetic diversity can arise as a result of mutation or during meiosis Flashcards
Gene Mutation
Achange in the base sequence of chromosomes
When can gene mutations arise
spontaneously during DNA replication and include base deletion and base substitution
Types of mutations
- Substitution
- Deletion
- Insertion
Gene Mutations: Base Substitution
A nucleotide in a DNA molecule is replaced by another nucleotide that has a different base
Gene Mutations: Base Deletion
A nucleotide is lost from the normal DNA sequence -> all the triplets are read differently (reading frame shift).
* May produce a dysfunctional protein
Gene Mutations: Base insertion
A single extra base is inserted into the DNA sequence -> all the triplets are read differently (reading frame shift)
* May produce a dysfunctional protein
Chromosome Mutations
- Changes in the whole set of chromosomes
- Changes in the number of individual chromosomes
Chromosome Mutations: Changes in the whole set of chromosomes
Condition Polyploidy: Occurs when organisms have 3 or more sets of chromosomes instead of 2.
* Occurs mostly in plants
Chromosome Mutations: Changes in the number of individual chromosomes
When individual homologous pairs of chromosomes fail to separate during meiosis = non-disjunction (results in gamete having more or less chromosomes, so body cells also have more or less chromosomes)
Why don’t all gene mutations cause a change in the sequence for the amino acid?
- The genetic code is degenerate
- The code is degenerate
Example of non-disjunction in humans
Down’s syndrome - individual has an additional 21st chromosome
Examples of chromosome mutations
- Hybridisation in wheat
What increases the risk of gene mutation
Mutagenic agents
Example of gene mutation
Sickle cell anaemia
