Epigenetics
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Epigenetics

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Epigenetics Presentation Transcript

  • 1. EPIGENETICS Prepared by: JCPIELAGO (reference: useful genetics couseraonline.org)
  • 2. EPIGENETICS (mostly imprinting) • Outline – Define ‘epigenetics’ – Functions – Mechanism – Genomic imprinting – Function (Parental Conflict Theory) – DNA methylation mechanism – Diseases affected by imprinting – Pedigrees
  • 3. EPIGENETICS (mostly imprinting) • Learning objectives – Define epigenetics – Diagram genomic imprinting (in several different ways) – Use the parental conflict theory to explain why specific gene are imprinted in the male or female parent – Explain how patterns of Methylation of CG dinucleotides are heritable – Track imprinting effects through a simple pedigree
  • 4. Epigenetics: Mechanisms of gene regulation that can be stably inherited through mitosis and (sometimes) meiosis, but can be established and released without changing the DNA sequence Wikipedia’s definition: The study of heritable changes in gene activity that are not caused by changes in the DNA sequence. This definition is much too broad – includes all forms of gene regulation
  • 5. Functions of epigenetic regulation • All our cells contain the same genes • Different cells and tissues differ in which genes they express. • These differences are created and maintained by gene regulation, not by changes in the DNA sequence (yes, there are exceptions…). • Some gene regulation has evolved to respond fluidly to changing conditions within the lifetime of a single cell. • Other regulation needs to be stable
  • 6. Functions of epigenetic regulation • Regulation that needs to be stable – Terminally differentiated cells – Specialized progenitor cells (stem cells) – Stably differentiated dividing cells – X inactivation (an extreme example)
  • 7. Mechanism of epigenetic regulation Some of the same processes used for other gene regulation must be heritable but not reversible especially regulation that changes how the gene’s DNA is packaged by chromatin proteins. – Modification of chromatin proteins – Methylation of DNA (removed in zygote, reestablished in the embryo and later); usually prevents gene expression.
  • 8. What Mendel found out about peas: 6. Each seed, and thus each organism, results from one ovum being fertilized with one pollen grain (not many, as some had previously thought) 7. The two parents make up equal contribution to the character 8. The effect of an allele is independent of whether it comes from the ovule or the pollen. Mendel’s results revealed the haploid-diploid sexual cycle
  • 9. What Mendel found out about peas: 6. Each seed, and thus each organism, results from one ovum being fertilized with one pollen grain (not many, as some had previously thought) 7. The two parents make up equal contribution to the character 8. The effect of an allele is independent of whether it comes from the ovule or the pollen. Mendel’s results revealed the haploid-diploid sexual cycle
  • 10. Genomic imprinting: For a few special genes, alleles inherited from the father are expressed differently than alleles inherited from the mother. Father Mother Offspring
  • 11. Genomic imprinting: For a few special genes, alleles inherited from the father are expressed differently than alleles inherited from the mother. Father Allele from the father Is inactive Mother Offspring
  • 12. Genomic imprinting: For a few special genes, alleles inherited from the father are expressed differently than alleles inherited from the mother. Allele from the father Is inactive Allele from the father Is inactive Father Mother Offspring
  • 13. Genomic imprinting: The identity of the allele doesn’t matter, just which parent it came from. Allele from the father Is inactive Allele from the father Is inactive Father Paternal imprinting Mother Offspring
  • 14. Genomic imprinting: Here’s an example of a different gene, where the maternal allele is always imprinted. Allele from the mother Is inactive Allele from the mother Is inactive Father Maternal imprinting Mother Offspring
  • 15. Genomic Imprinting
  • 16. Genomic Imprinting
  • 17. Genomic Imprinting Notes: 1. The alleles behave normally in meiosis; only their expression in the offspring is affective. 2. Dominance is meaningless… imprinted loci are effectively HEMYZTGOUS.
  • 18. What is the function of genomic imprinting? (Why did it evolve?) The best explanation: Parental Conflict Hypothesis
  • 19. Parental Conflict Theory
  • 20. Parental Conflict Theory
  • 21. DNA Methylation
  • 22. DNA Methylation
  • 23. Think about how genomic imprinting works: All of the inherited imprinting marks are erased when the germ line develops. A gene that’s evolved to be paternally imprinted has a sequence-tag that says: If you’re male, methylate this gene before you make gametes. A gene that’s evolved to be maternally imprinted has a sequence-tag that says: If you’re female, methylate this gene before you make gametes.
  • 24. Imprinting has evolved to a state where both parents’ interest are roughly in balance. But it causes problems if something goes wrong with normal inheritance: a.) Defective allele from the non-imprinted parent b.) Deletion from the non-imprinted parent c.) Both alleles inherited from one parent (‘uniparental disomy’) b.) and c.) are especially bad because imprinted genes are often clustered together on one chromosome.
  • 25. Imprinting causes problems if something goes wrong with the normal inheritance: One segment of chromosome 15 includes genes that are paternally imprinted and genes that are maternally imprinted.
  • 26. Imprinting causes problems if something goes wrong with the normal inheritance: One segment of chromosome 15 includes genes that are paternally imprinted and genes that are maternally imprinted. Inherit deletion from father Inactive alleles From mother (M-I) Prader-Willi Syndrome Inherit deletion from mother Inactive alleles From father (P-I) Angelman Syndrome