Epigenetics

Epigenetics - heritable effects resulting from alteration of DNA (not in DNA sequence) or chromatin during gametogenesis

• Conrad Waddington, 1942

• EPIGENETICS DOES NOT CHANGE THE DNA SEQUNCE__ONLY MUTATION CAN DO THAT

Genomic printing - phenomenon where a gene’s expression depends on the parental origin of a gene copy

Gene silencing - a gene is not expressed

• Transcriptional gene silencing - transcription is blocked because the gene occurs in heterochromatin )transcriptional enzymes cannot access perfectly normal genes)

• Post-transcriptional gene silencing - mRNA from a transcribed gene is destroyed or blocked, transilation does not occur

• RNAi pathway - microRNA or small interfering RNA blocks translated of targeted mRNA

• Used as defense against viruses, during development, and to regulate gene expression

DNA methylation can also cause gene silencing

• Addition of methyl groups (CH3 to CG dinucleotides of imprinted DNA areas)

• Methylated C nucleotides prevent attachment of RNA pol and transcription factors

• Methylated DNA patterns transmitted during DNA replication