5.4 Variability & Genetics- Mutations

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  • Created by: Rebecca
  • Created on: 19-06-11 18:57


  • Mutation is a change in the amount, structure, or arrangement of DNA in an organism.
  • It may affect a single gene or a whole chromosome.
  • It usually occurs in somatic (body) cells.
  • Mutations occur spontaneously.
  • Only those that occur during the production of gametes can be inherited.
  • Most mutations are infrequent and have relatively little impact on evolution than other sources of variation.
  • They occur more frequently in organisms with a short life cycle, where meiotic divisions take place regularly.
  • Mutations are more likely to occur (mutation rate increases) if the organism is exposed to ionising radiation or mutagenic chemicals.

Mutations can occur in two ways:

  • DNA is not copied properly. Sometimes new chromosomes are produced fault due to a mistake during replication. They are often only small errors, but they can be serious if located on important genes. They are called Gene-Mutations or Point Mutations.
  • Chromosomes are damaged and break. Broken chromosomes usually repair themselves but they may do this incorrectly. This may affect large number of genes and is called a Chromosome Mutation.

Gene Mutations:

  • Change in structure of a DNA molecule, specifically in the base pairs within the genes.
  • Produces a different allele of a gene.
  • Rates of mutation vary between organisms, and between genes within an organism.
  • The changes can be: duplication, insertion, deletion, insertion or substitution of bases.
  • The result is a modified polypeptide.

How Can Mutations Cause a Change in the Phenotype?:

  • Any change to one or more of the nucleotides, or any rearrangement of the sequence, produces an incorrect sequence of amino acids in the protein it makes.
  • The protein is often an enzyme. This enzyme may then be unable to catalyse a certain reaction.
  • An example of this is if the enzyme is missing to catalyse the production of pigment in an organism's skin, they will lack pigment, which is known as being Albino.

Sickle Cell Anaemia:

  • This is a gene mutation in the gene producing haemoglobin.
  • The replacement of one base in the DNA molecule results in the wrong amino acid being produced and incorporated into two of the polypeptide chains that make up the


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