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10 Cards in this Set

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Define Epigenetics and Epigenome

Epigenetics - study of heritable changes in gene expressionwithout change in DNA sequence


(involves DNA remodelling - methylation +histones)




Epigenome - The total collection of epigenetic settings across a genome

Explain the role of chromatin remodelling processes in theregulation of gene activity

DNA methylation


add CH3 to 5' carbon of cytosine (ONLY CYTOSINES IF FOLLOWED BY A GUANINE) within CpG islands of promotor regions


(patterns can be tissue/gene/person specific)




works with histones to regulate chromatin structure and gene expression




high methylation = inactive transcription (eg X inactivation)

How does DNA Methylation occur?

DMNT (DNA methyltransferases) meditated


(reversed by DNA demethylases)




DMNT1 maintains existing methylation pattern




DMNT3A/3B - de novo


Important in puberty epigenetic programing


resets epigenetic marks (demethylation then methylation)




*chart with hemi meth (passive demethylation) for just DMNT1, active for DMNT3A/3B

When/how does DNA methylation change during development?

middle - primordial, fertilised oocyte, sperm(slight up), egg(slight down), placenta/yolk sac




low - gonadal differentiation, blastocyst




high - somatic cells (down to PCGs)

What are the 2 types of Histone modifications and when do they occur?

Histone acetylation/deacetylation


occurs when opening/condensing chromatin




Acetylation - involves HATs


acetyl group transferred from histone lysine->open state


pos charge of histones NEUTRALISED




Deacetylation - involves HDACs


reverses acetylation


OVERALL CHARGE OF HISTONES POSITIVE





For Chromatin remodelling what state of acetylation and methylation must occur for transcription?

Acetylation follows opposite of DNA methylation

DNA methylation with histone deacetylation = CLOSING (therefore no transcription)

DNA demethylation with histone acetylation = OPENING (therefore transcription can occur)

Give examples of epigenetic phenomena and explain theirmechanisms and consequences

reprogramming in early embryo




gametogenesis

Explain the principles of genomic imprinting and Xinactivation

most genes are monoallelic (one gene expressed)




silencing of one allele according to parent = GENOMIC IMPRINTING




(reversible, can be switched between generations


eg. man receives inactive allele from mother but it is activated for mans generation)




X inactivation - to allow same dosage in M/F


stable across mitosis but not across generations

Discuss how primary and secondary epimutations may cause disease

primary - without base sequence change, reprogrammed chromatin state. may be induced by environment




secondary - caused by genetic mutation at defined locus, may involve gene/cis-acting regulatory sequence, determine disease phenotype

Outline examples of genomic imprinting disorders and explainthe causes, pathogenesis and molecular basis of each disorder

Imprinted gene cluster - Angelman (AS) + Prada-Willi (PWS) syndromes


neurodevelopmental disorders (cluster on chrom 15q11-13)


AS - severe mental disability, microcephaly (laughter and smiling) deletions from MATERNAL



PWS - mild intellectual disability, hyperphagia (obesity) deletions from PATERNAL