OCR A2 Biology Mutations revision notes

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  • Created by: Paige
  • Created on: 06-05-11 18:09
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Random change to genetic material, either DNA or chromosomes
DNA mutations include base deletions, insertions or substitutions or
triplet repeats or deletions
Chromosome structures can suffer deletions, duplications, inversions or
They occur during DNA replication before nuclear division by mitosis
(somatic, not inherited) or meiosis (inherited)
Mutagens ­ factors that cause mutations:
UV light
X rays
Gamma Rays
There are two main classes of DNA mutations:
1. Point mutation ­ one base replaces another (substitution)
2. Insertion/deletion of one or more base causes a frameshift (triplet
code altered)
Genetic Diseases
Cystic Fibrosis 70 % of cases due to deletion of a triplet so one of the 1480
amino acids in the normal polypeptide is missing
Sickle cell anaemia Point mutation on codon 6 of the gene for the beta
polypeptide chains of haemoglobin. This causes the amino acid valine to be
inserted instead of glutamic acid in the chain.
Tumours A point mutation in a protooncogene (growth promoting gene) can turn
it into an oncogene which cannot be switched off resulting in uncontrolled growth
of cells
Huntington's Expanded triple nucleotide repeats (`stutter'), normal Huntington's
protein contains CAG repeats excessive numbers of repeats affects the protein

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Mutations 2
Mutations with neutral effects
Genes altered by a change in their base sequence result in different
alleles (forms of a gene)
If the base change results in a change in protein structure a different
characteristic may occur
New characteristics that are neither favourable or harmful are described
as NEUTRAL e.g. ability to smell honeysuckle, hand clasping, attached
New characteristics may be favourable e.g.…read more


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