GiM: Genomic Imprinting and Epigenetics Flashcards
What is Androgenesis and what can it result in?
Development in which the embryo contains only paternal chromosomes (failure to develop embryo)
Can result in Hydratidiform Mole= 46XX, proliferation of abnormal trophoblast tissue, can become malignant.
What is Parthogenesis?
Reproduction from an ovum without fertilization (failure to develop extraembryonic features like trophoblast and yolk sac)
What is genomic imprinting?
A mechanism that ensures the functional non-equivalence of the maternal and paternal genomes.
Not encoded in the DNA nucleotide sequence i.e. EPIgenetic
Deletion of Chromosome 15 found in both Angelman and Prader-Willi Syndromes which is always de novo (so recurrence risks very low). But what is the difference?
Angelman= deletion of chromosome 15 from MATERNAL side. (could also be to do with uniparental disomy where there is a lack of maternal 15q11-13 contribution) Prader-Willi= deletion of chromosome 15 from the PATERNAL side. (also could be uniparental disomy)
What do imprinted genes show?
Monoalleic Expression (when only one allele of the gene is actively transcribed).
What is the EPIgenetic difference between maternal and paternal alleles?
Maternal allele is silenced after methylation.
Paternal allele is active after methylation.
There is a fetal-maternal growth conflict. So perhaps maternal and paternal genes influence the growth of a baby differently. How does this influence Inulin-like growth factor 2?
Hypomethylation= reduced IGF2 –> Russel Silver Syndrome (growth retardation, triangular face, asymmetry)
Hypermethytlation= increased IGF2 –> Beckwith Wiedemann syndrome (fetal overgrowth, organomegaly, tumour risk)
How is X-inactivation (lyonisation) different to genomic imprinting?
- Whole X chromosome is silenced
- Random choice of parental chromosome
- Occurs early in embryogenesis (blastocyst), at a time where there are a small number of precursor cells and so random SKEWING is possible
