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Genomic imprinting
Although we inherit two copies
of all genes, except those that reside
on the sex chromosomes, there is a
subset of these genes in which only
the paternal or maternal copy is
functional. One gene copy is silenced
depending on the sex of the
transmitting parent
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Over 30 imprinted genes
have been discovered since
the early 1990’s
Example 1: The insulin-like growth
factor 2 (Igf2) and H19 genes.
The sole purpose of H19 appears to be
to 'imprint' Igf2.
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What is genomic imprinting?
The expression or
the inactivation of either
the maternal or paternal
allele of a particular
locus.
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Estimates of the number
of imprinted genes in the
mammalian genome range from
less than 100 to greater than
200.
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What modification of
DNA is thought to be
responsible for genomic
imprinting?
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Some examples of possible imprinted
diseases include:
Huntington's disease
Cystic fibrosis
Prader-Willi and Angelman syndromes
Birth defects such as spina bifida
Some cancers such as Wilm's tumor
(associated with loss of methylation of
the Igf2 insulin-like growth factor
gene)
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11p15.5
Beckwith– Wiedemann
syndrome (BWS)
-- a growth disorder with risk of
childhood cancers
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Paternal 'antisense'
transcripts are being found
associated with maternally
expressed imprinted genes.
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