Ryan Yerger BIOL-101THE IMPORTANCE OF GENOMIC IMPRINTING
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
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.
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.
http://www.youtube.com/watch?v=0ff4o6ttkmU Clip going into short detail of each syndrome.
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.
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.
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.
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.