Mutations
Mutations
Mutation refers to any change in the nucleotide sequence as a result of a failure of the system to revert the change. Thus, the altered sequence is permanent and heritable. Because mutations are random changes, they are expected to be mostly deleterious, but some may be beneficial in certain environments. In general, mutations are the main source of genetic variation, which is the raw material for evolution by natural selection.
Gametic Mutations
- are mutations that occur in the process of the formation of gametes. These will be inherited by any offspring produced by fertilisation of the gametes involved. If the zygote survives and is successful the new alleles created by the mutation are available to the gene pool and may become established in that gene pool.
Somatic mutations
- are mutations that occur in somatic (Body) cells. These mutations only affect cells in that area of the body and are not inheritable.
Mutations
There are many different types of Mutation This video introduces gene mutations and Chromosome mutations.
Gene Mutations
Affecting only one gene.
Point Mutations
Substitution mutations may make no change to the amino acid sequence of a gene. These are silent mutations as they have no affect on the allele produced. If, however, a different amino acid is coded for it may result in a new protein which may represent a new allele.
Insertion or deletion mutations will cause a frameshift in reading the codons of a protein. This may seriously affect the protein produced.
Sickle anaemia
Sickle Cell Anaemia is an example of a single substitution mutation. There is selection for the Heterozygous genotype as this provides some protection against malaria
Frameshift
Caused by the insertion or deletion of a nucleotide.
Cystic Fibrosis
Cystic Fibrosis is a result of Two frameshift mutations (one is the insertion of two nucleotides and the other deletion of one nucleotide) in the CFTR genes result in cystic fibrosis.
Chromosome Mutations(Block Mutations)
-are alterations that affect whole chromosomes and whole genes rather than just individual nucleotides. These mutations result from errors in cell division that cause a section of a chromosome to break off, be duplicated or move onto another chromosome.
Chromosome Block Mutations
- deletion is where a section of a chromosome is removed.
- translocation is where a section of a chromosome is added to another chromosome that is not its homologous partner.
- inversion is where a section of a chromosome is reversed.
- duplication occurs when a section of a chromosome is added from its homologous partner
Aneuploidy
- a condition of having missing or extra chromosomes.
Downs Syndrome
Trisomy 21 - an extra chromosome 21 results in a child with Downs Syndrome
Turners Syndrome
Turners Syndrome is an example of aneuploidy where there is only one 'X' Chromosome.
Karyotype for Turners Syndrome.
