Epigenetics and Abnormal Gene Expression Flashcards
What is higher-order DNA structure?
Folding and organizing DNA beyond the double helix into chromatin and chromosomes to regulate gene expression and fit in the nucleus.
What are nucleosomes?
DNA wrapped around histone protein cores; they are the basic units of chromatin structure.
How is chromatin further organized?
Nucleosomes form 30 nm fibers, looped domains, and chromosomal territories within the nucleus.
What is X-chromosome inactivation?
The silencing of one X chromosome in female cells to equalize gene dosage with males.
What initiates XCI?
The XIST gene produces RNA that coats the X chromosome, triggering silencing through epigenetic changes.
What epigenetic changes are involved in XCI?
DNA methylation, histone modifications, and chromatin condensation.
When does XCI occur?
During early embryonic development, around the blastocyst stage.
How is imprinting maintained?
Through DNA methylation at imprinting control regions and histone modification.
What is genomic imprinting?
Parent-specific gene expression due to epigenetic silencing of one allele.
Example of an imprinted gene?
IGF2 is expressed only from the paternal allele.
What is UPD?
Uniparental disomy - A condition where both chromosomes in a pair come from the same parent.
What is isodisomy?
Two identical copies of a chromosome from one parent.
What is heterodisomy?
Two different homologous chromosomes from one parent.
Why is UPD problematic?
It can disrupt imprinting, leading to overexpression or lack of essential genes.
What causes Prader-Willi Syndrome?
Loss of paternal gene expression on chromosome 15 via deletion, maternal UPD, or imprinting error.
What causes Angelman Syndrome?
Loss of maternal UBE3A gene function on chromosome 15 due to similar mechanisms.
How does epigenetic dysregulation lead to cancer?
Hypermethylation of tumor suppressor genes or altered histone modification can silence crucial regulatory genes.
Example of epigenetically influenced cancers?
Colorectal and breast cancers often involve abnormal DNA methylation patterns.
