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10 Cards in this Set

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  • Back

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


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


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