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Two forms of muscular dystrophy are caused by deletion mutations in the dystrophin gene. (Adapted, with permission, from Hoffman and Kunkel 1989;
photos, reproduced with permission, from Arthur P. Hays.)
A. The relative position of the dystrophin gene within the Xp21 region of the X chromosome. An enlargement of this locus shows the 65 exons (light blue)
and introns (dark blue) defining the gene with approximately 2.0 106 base pairs. Transcription of the gene gives rise to mRNA (approximately 14 103 base
pairs), and translation of this mRNA gives rise to the protein dystrophin (mol wt 427,000). Expression of dystrophin in a normal muscle is shown in an
immunoperoxidase
photo of
at the
right.
Source:stain
Diseases
Nerve and Motor Unit, Principles of Neural Science, Fifth Editon
B. A deletion
of
genomic
DNA
encompassing
only TM,
a single
exon results
in the clinically
Duchenne
muscular
dystrophy.
A larger
Citation: Kandel ER, Schwartz JH, Jessell
Siegelbaum
SA, Hudspeth
AJ, Macksevere
S. Principles
of Neural
Science,
Fifth Editon;
2012deletion
Available
encompassing fourat:exons
results
in
the
clinically
milder
Becker
muscular
dystrophy.
In
both
cases
the
gene
is
transcribed
into
mRNA,
and
the exons
http://mhmedical.com/ Accessed: August 03, 2017
flanking the deletion
are
together. 1.Education.
If a single All
exon
is deleted
and a nonintegral set of codons is missing, the borders of neighboring exons may
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2017 McGraw-Hill
rights
reserved
not match, causing the translational reading frame to shift. As a result, incorrect amino acids are inserted into the growing polypeptide chain until an