Consequences of
DNA
mutations
depend on their position in the gene region
For this hyhypothetical gene, the
complete gene includes protein-coding
exons, as well as intervening introns, and
flanking control regions
such as upstream (5')
promoters
and enhancers in
upstream
& downstream (3')
regions.
m1:
Mutations in
the
promoter region may
affect gene transcription may lead to non-functional
(null)
alleles.
m2:
Mutations
in exons,
if they result in the substitution of an amino acid in the active
site or
other critical region of the protein, also lead to alleles with modified
(reduced)
functionality.
m3:
In
contrast, exon mutations that result in
changes outside the active
sites or
at 3rd codon
positions may
have little or no effect on gene
function.
These
mutations are called silent
(if
the amino acid is unchanged) or neutral (if the change
has
no effect).
m4: Mutations
at critical positions near intron
/
exon junctions may
affect mRNA
splicing and
lead to
the deletion or retention of entire exons, and result in null alleles.
m5:
Mutations that occur in non-coding
introns, or
m6:
5'
or 3' flanking
portions
of the gene, may
have little or no effect on gene
function.
Figure
modified from Klug & Cummings 1997; All text
material
© 2014 by Steven M. Carr