Epigenetics Overview and Concepts
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Questions and Answers

What is the primary effect of methylation on cytosine in DNA?

  • It converts cytosine to thymine (correct)
  • It promotes gene expression
  • It increases mutation rates in all dinucleotides
  • It enhances chromatin remodeling

How does chromatin remodeling affect gene expression?

  • It causes gene silencing
  • It allows access to regulatory sequences (correct)
  • It decreases the mutation rate
  • It only affects heterochromatin

Which process describes the transcriptional inactivity of one allele based on parental origin?

  • Mesoderm differentiation
  • Gene duplication
  • Genomic imprinting (correct)
  • Chromatin remodeling

What is the mutation rate increase at CG dinucleotides compared to other dinucleotides?

<p>12 times higher (A)</p> Signup and view all the answers

What is a characteristic feature of imprinted alleles?

<p>They are heavily methylated (A)</p> Signup and view all the answers

What role does histone hypoacetylation play in gene transcription?

<p>It inhibits the binding of transcription-promoting proteins (D)</p> Signup and view all the answers

Which statement accurately reflects the principle of genomic imprinting?

<p>Imprinting leads to one functional copy of a gene depending on the parent. (C)</p> Signup and view all the answers

What is the primary result of genomic imprinting?

<p>One allele is expressed while the other is methylated and inactive. (B)</p> Signup and view all the answers

Which mechanism is NOT associated with imprinting disorders?

<p>Mendelian inheritance (D)</p> Signup and view all the answers

What occurs in uniparental disomy (UPD)?

<p>A child inherits both chromosome copies from one parent. (C)</p> Signup and view all the answers

Prader-Willi syndrome is primarily caused by which genomic alteration?

<p>Paternal chromosome deletion. (C)</p> Signup and view all the answers

Which of the following features is NOT associated with Angelman syndrome?

<p>Hypotonia. (B)</p> Signup and view all the answers

How does isodisomy differ from heterodisomy in uniparental disomy?

<p>Isodisomy involves two identical homologs from one parent. (C)</p> Signup and view all the answers

Which of the following best describes the critical region deleted in Prader-Willi and Angelman syndromes?

<p>It includes genes that are transcriptionally inactive from the maternal chromosome. (D)</p> Signup and view all the answers

What is the clinical significance of uniparental disomy in imprinting disorders?

<p>It can increase the risk of autosomal recessive disorders. (C)</p> Signup and view all the answers

What is the main characteristic of genomic imprinting?

<p>One copy of a gene is inactive depending on the parent it came from. (B)</p> Signup and view all the answers

How is the expression of imprinted genes primarily controlled?

<p>Through a process of methylation. (C)</p> Signup and view all the answers

What happens to the methylation tags on imprinted genes during gametogenesis?

<p>They are reset before fertilization. (A)</p> Signup and view all the answers

Which of the following statements about uniparental diploidy is true?

<p>It is considered lethal. (C)</p> Signup and view all the answers

Why is only one allele expressed for imprinted genes despite inheriting two?

<p>One allele is silenced based on its parental origin. (D)</p> Signup and view all the answers

What is the effect of methylation on gene expression?

<p>It prevents gene expression. (A)</p> Signup and view all the answers

In what way does genomic imprinting demonstrate epigenetic control?

<p>By marking genes with their parental origin. (C)</p> Signup and view all the answers

What is a consequence of imprinting that leads to its significance in development?

<p>It can result in abnormal phenotypes if disrupted. (D)</p> Signup and view all the answers

Flashcards

Genomic Imprinting

A process where only one copy of a gene is active, depending on which parent it came from.

Imprinted Genes

Genes where the expression of one parent's allele is suppressed.

Uniparental Diploidy

Condition where only one parent's alleles are present (usually lethal).

Methylation

Adding methyl groups to a gene to prevent its expression.

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Imprinting Center

Region of a chromosome that orchestrates the gene inactivation of specific imprinted genes (especially during gametogenesis).

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Epigenetic Imprinting

The unequal expression of maternal and paternal alleles of a gene.

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Gametic Origin

Parental origin of a gamete (maternal or paternal).

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Epigenetic Tags

Chemical modifications that affect gene expression without changing the DNA sequence, such as methyl groups.

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5-methylcytosine mutation

A methylated cytosine (5-methylcytosine) can lose an amino group, changing to thymine, causing a mutation.

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CG dinucleotide mutation rate

Mutations at CG sites are significantly higher than other dinucleotide sequences in humans.

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Chromatin remodeling

Dynamic changes in chromatin structure, allowing DNA access to transcriptional machinery.

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Heterochromatin boundary maintenance

Essential for maintaining the stable borders of heterochromatin regions in the genome.

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Uniparental Disomy (UPD)

A condition where a child inherits two copies of a chromosome from one parent instead of one from each parent.

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Isodisomy

A type of UPD where both copies of a chromosome are identical (same homolog).

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Methylation and gene silencing

Methylation of DNA and related chromatin modifications can inactivate genes.

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Heterodisomy

A type of UPD where the two chromosomes inherited from a single parent are different homologs.

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Epigenetic inheritance

Heritable changes in gene expression that do not involve changes to the DNA sequence.

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Prader-Willi Syndrome (PWS)

A genetic disorder often caused by a missing segment of chromosome 15 inherited from the father.

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Angelman Syndrome

A genetic disorder often caused by a missing segment of chromosome 15 inherited from the mother.

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Chromosome 15 Imprinting

The process of expression silencing (turning off) of certain genes on chromosome 15 depending on parental origin

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Imprinting Disorders

Conditions that arise from disruptions in the imprinting process, affecting the appropriate gene expression

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Study Notes

Epigenetics Definition

  • Epigenetics encompasses all processes that alter gene expression without changing the DNA sequence.
  • These changes are heritable, impacting how genes are expressed and how chromosomes function.

Epigenetic Problems

  • How do keratinocytes differentiate into only skin cells?
  • How do different adult stem cells know their fate?
  • How can identical twins have unique traits like different hair colours or eye colours?
  • How can offspring inherit only maternal or paternal traits?
  • How can females inactivate one X chromosome per cell?
  • How can acquired traits be passed on to offspring?

Epigenetic Reprogramming in the Early Embryo

  • Egg and sperm cells have unique epigenetic marks.
  • During fertilization, the zygote undergoes reprogramming, erasing most of these inherited marks in the genome.
  • By the blastocyst stage, cells of the inner cell mass have epigenetic marks re-established, necessary for cell differentiation and body development.
  • Epigenetic marks are re-established in the inner cell mass's descendants, establishing different cell lineages.

Epigenetic Reprogramming on Gametogenesis

  • Genome-wide demethylation occurs during germ cell development.
  • This erasure of epigenetic marks is followed by comprehensive de novo DNA methylation.
  • This resetting establishes global patterns in DNA methylation and gene expression.

Establishment of Constitutive Heterochromatin

  • Centromeres rely on a specialized histone H3 variant—CENP-A.

X-Chromosome Inactivation

  • X inactivation involves silencing one X chromosome in female cells through the action of XIST RNA.
  • This prevents over-expression of X-linked genes.

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Genetics Notes Exam 4 PDF

Description

Explore the fascinating world of epigenetics with this quiz. Learn about how gene expression is altered without changing the DNA sequence, the processes leading to different traits in identical twins, and the reprogramming that occurs during early embryonic development. Test your understanding of key concepts and their implications in biology.

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