Epigenetics Epigenetics Changes in gene expression that are not caused by a change in nucleotide sequence Meaning is placed upon a gene without altering ith lt t i M i l the nucleotide sequence d i Often triggered by environment Examples of Epigenetics 1 Differentiation 2 X inactivation 3 Genomic imprinting 4 A close up look at specific disorders IUGR Prader Willi syndrome and Angelman syndrome Epigenetics 1 Differentiation The process of cells specializing during development Genes are silenced or turned off The addition of methyl groups CH3 to cytosine The addition of methyl groups CH to cytosine inactivates the gene All cells of the body have the same genome but different genes are turned off in different cell types X inactivation An entire chromosome with the exception of a few genes is methylated in females Creates barr body Random process a do p ocess Maternally derived X is inactivated in some cells paternally derived X is inactivated in other cells Once it occurs all descendants from that cell will have the same X inactivated No difference in homozygotes but X inactivation may be visualized in heterozygotes Observing X inactivation Anhidrotic Ectodermal Dysplasia Epigenetics 2 Observing X inactivation Calico Cat Genomic Imprinting A gene is expressed when inherited from one parent and is silenced when inherited from the other parent The gene that is silenced is said to be imprinted The gene that is silenced is said to be imprinted So parental origin of a gene influences Function unknown may play a role in phenotype development Genomic Imprinting Imprints maintained in mitotic divisions but lost in meiosis Gene remains imprinted during mitosis of somatic cells somatic cells As if the gene remembers which parent it came from However imprints are lifted and reset for the sex of the parent during meiosis Epigenetics 3 Genomic Imprinting Importance of Genomic Imprinting Experiments suggest that it takes two opposite sex parents to produce a healthy embryo Genes from female parent direct different d ff d f f l activities from the genes of the male parent Certain assisted reproductive technologies may produce imprinting disorders Intrauterine growth retardation IUGR IUGR by definition is when a fetus does not receive adequate nutrition and is born very small The near starvation environment in utero is linked to an increased incidence of cardiovascular disease later in life It also appears to alter gene expression involved with glucose metabolism since these individuals are at risk for diabetes too Epigenetics 4 Prader Willi Syndrome PWS Small at infancy Develop obsession with food early in childhood Become severely obese Caused by a gene deletions on chromosome b l 15 Angelman Syndrome AS happy puppet sydrome Poor coordination convulsions severe MR Caused by the gene deletions on the same region of chromosome 15 f h i PWS and AS It depends upon which parent the chromosomal deletions were inherited from In AS the normally active maternal genes are deleted paternally inherited copies are deleted paternally inherited copies are imprinted In PWS the normally active paternal genes are deleted maternally inherited copies are imprinted Epigenetics 5 Video Ghost In Your Genes You may want to print off transcripts to be able to follow along in class i Transcripts can be found at d http www pbs org search search results ht ml q ghost in your genes transcripts b f Epigenetics 6
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