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specialties are two rare forms of mental retardation, Prader-Willi
syndrome and Angelman's syndrome, which are thought to be caused
by deletions on chromosome 15. If the missing gene occurs on the
mother's chromosome, Angelman's syndrome is the result. If it occurs
on the father's chromosome, Prader-Willi syndrome is the consequence.
This phenomenon in which defects occur depending on whether the
mutation takes place on the either the mother's or father's chromosome
is called parental imprinting.
similar mechanism affects some cancer cells, LaSalle explains, except
that the mutations that cause genetic defects in babies are inherited
or occur in the egg or sperm. Mutations that cause tumors to grow
in adults, however, occur in individual cells.
genes within imprinted chromosomal regions are only expressed on
one chromosome, a deletion on the other chromosome in a single cell
would result in the total absence of expression of that gene,"
LaSalle explains. "Many imprinted genes are involved in basic
mechanisms of cell growth, so the loss of such genes in cells could
right: Postgraduate researcher Carlo Lagdamen at the laser-scanning
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