Changes to the DNA
of the genome - what is a mutation? - what are genetic variants?
Doc Brown's Biology exam study revision notes
There are various sections to work through, after 1 they can be read and studied in any order.
of biology notes on genetic variation, and the causes, formation and
consequences of mutations
(2) Changes can happen to the DNA
of the genome - mutations - genetic variants
Sometimes DNA may mutate, meaning a random change occurs in
sequence of an organism.
It is possible for the mutation to be inherited.
This automatically changes the sequence of bases in the DNA molecule.
Therefore the gene expression may be altered or
Here we are dealing with a different version of
the gene - a genetic variant (also called an allele).
Any mutation changes the sequence of bases
in a strand of DNA which produces a different form of the gene
(allele), and is called a genetic variant.
In the course of evolution advantageous mutations
are more likely to be inherited through successive generations.
All the different versions of genes are called genetic variants or
alleles and are formed by mutations (but do not assume they
are all harmful to the functioning of an organism!).
Despite the frequency of mutations, most have no
or very little effect on the protein synthesised in the ribosomes.
change in protein structure is usually slight and harmless and its
function or appearance is relatively unaffected.
However, certain mutations can have quite
an effect on a protein with serious consequences.
This result of this genetic variant may code for a different
sequence of amino acids and consequently may change the shape of the final protein structure and its activity.
e.g. theoretically, for an enzyme
(protein), its activity
may be increased, decreased or completely inhibited its action.
A mutation might even lead to coding for a
different amino acid and hence a different protein is produced.
The protein might not be useful or
potentially harmful and treated as a 'foreign' substance by the
If the protein is no longer the right
shape it might not be able to perform its function e.g.
(i) an altered shape might mean an
cannot perform its catalytic action because the substrate
can't lock into the active site - see diagram below (from my
Enzymes - structure and functions
(ii) If substances like collagen, the
main structural protein molecule in the connective tissues
of your body, isn't formed properly, muscle tissue can be
weakened or completely useless in providing physical support
for an organisms body.
Genetic variants can be inherited from one
generation to another e.g. mother to child.
more on the consequences of
mutations (on this page)
effects of non-coding DNA (on this page)
evolution page for
lots more notes on variation
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