2. IMPRINTING
Most genes.
Inherit working copies.
One from mom, other
from dad.
Imprinting.
Inherit one working
copy.
Depending on gene,
copy from mom or dad is
epigenetically silenced.
Silencing occuring
through addition of
methyl groups during
egg/sperm formation
3. IMPROPER IMPRINTING
Individual typically has one active
copy.
Improper imprinting can lead to two
active copies or two inactive copies.
Developmental abnormalities, cancer, etc.
Prader-Willi and Angelman
Syndrome.
Very different, but linked to chromosome
15.
4. PRADER-WILLI AND ANGELMAN
Prader-Willi Syndrome Angelman Syndrome
Symptoms Symptoms
Learning difficulties, learning difficulties,
short stature, compulsive speech problems,
eating. seizures, jerky
Missing gene activity movements, unusually
happy disposition.
that comes from Father.
Missing gene activity that
Father’s copy missing,
comes from Mother.
or two maternal copies.
Mom’s copy is missing,
two paternal copies.
5. http://www.youtube.com/watch?v=0ff4o6ttkmU
Clip going into short detail of each syndrome.
7. GENETIC CONFLICT HYPOTHESIS
supposes that imprinting grew out of a
competition between males for maternal
resources.
Is in the interest of the Father’s genes to
produce larger offspring.
Best for the Mother’s genes if all of offspring
survive to adulthood and reproduce.
8. GENETIC CONFLICT HYPOTHESIS CONT’D
Many imprinted genes deal with growth and
metabolism.
Paternalimprinting favors larger offspring.
Maternal imprinting favors smaller offspring.
Maternal and Paternal work in same growth
pathways.
Sets up epigenetic battle between parents.
Parental tug-of-war.
9. BECKWITH-WIEDEMANN SYNDROME
Igf2 gene codes for a hormone that
stimulates growth during embryonic and fetal
development.
Methyl tags usually silence maternal Igf2 gene.
DNA mutation (epimutation) can activate it.
Causes BWS.
Most common feature is over-growth.
Babies born larger than 95% of peers.
Increased risk of cancer.
10. BECKWITH-WIEDEMANN SYNDROME CONT’D
Occurs 1 in 15,000 births.
Babies conceived in laboratories with help of
artificial reproductive technology (ART), rate
of BWS goes up to 1 in 4,000.
Safety of ART laboratory procedures into
further investigation.
