3.
What
causes mutations?
Doc Brown's Biology exam study revision notes
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Sub-index of biology notes on genetic variation, and the causes, formation and
consequences of mutations
(3) What
causes mutations?
Completely random mutations are relatively uncommon, in DNA code
copying, it is estimated that there is a 1 in 109 (1 in a
billion) chance of a mutation, though other factors can come into play
to increase this e.g. exposure ionising radiation and ingesting
carcinogenic molecules..
Mutations are happening all the time and can occur
quite spontaneously - a random event.
There are various different ways that the rate
of mutations can
increase and change the base sequence in DNA e.g.
A mutation can happen if an error occurs in
chromosome replication (DNA replication) i.e. it might not be as
perfect as that shown in the diagram below (see
DNA and RNA structure and Protein Synthesis).
The chance of a mutation is increased if an
organism is exposed to certain chemicals, particularly those known as
carcinogenic substances e.g. some constituents of tobacco tar.
A carcinogen is defined as any
substance (e.g. carcinogenic chemical), radionuclide, or radiation that promotes carcinogenesis,
the formation of cancer.
This may be due to the ability of the
substance or radiation to damage the genome or to the disruption of
cellular metabolic processes.
Some molecules cause mutations by interfering
with the unzipping of DNA and producing errors in the replication.
Radiation from radioactive materials is
particularly effective in causing mutations, hence the dangers
associated with exposure to alpha, beta and gamma ionising radiations.
The energy of the particles is great enough to
break chemical bonds, inducing changes in the molecular structure of
DNA.
See
Alpha, beta & gamma radiation -
,dangers of radioactive emissions - health and safety issues and ionising radiation
gcse physics revision notes
Summary of learning objectives and key words or phrases
Know examples of what causes mutations including radioactivity
- ionising radiation,
carcinogenic chemicals, and mutations caused by random errors in DNA replication
after the double helix splits into two strands to form the template for DNA
replication.
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