Genetics Chapter 21

What is epigenesis?

How an embryo develops

What is genetics?

The study of genes and heredity

When discussing epigenetics, what do we primarily talk about?

Changes that are heritable

What molecular processes can lead to epigenetic changes?

• Changes in chromatin structure, which alter gene expression

• Molecular mechanisms that alter chromatin structure

What molecular mechanisms that alter chromatin structure can lead to epigenetic changes?

• Changes in patterns of DNA methylation

• Chemical modification of histone proteins

• RNA molecules that affect chromatin structure and gene expression

What is DNA methylation?

addition of methyl groups to nucleotide bases; a common epigenetic modification of chromatin

What is the most common DNA methylation?

Methylation of cytosine to produce 5-methylcytosine

How is DNA methylation stably maintained?

Through DNA replication; allows for inheritance

What are epigenetic changes responsible for in honeybee queens?

Royal jelly suppresses Dnmt3, which normally methylates DNA. This leads to expression of genes that encode characteristics of the queen

How does detecting DNA methylation lead to epigenetic changes?

By cutting the DNA with restriction endonucleases that are sensitive to DNA methylation

How does bisulfite sequencing lead to epigenetic changes

By sequencing genomic DNA with and without bisulfite treatment, researchers are able to determine the locations of all copies of 5-methylcytosine in the DNA

How can histone modifications lead to epigenetic changes?

More than 100 different posttranslational modifications of histone proteins REVIEW THIS SLIDE

Modifications include addition of?

• Phosphates

• Methyl groups

• Acetyl groups

• Ubiquitin

What can maintenance of histone modifications result in?

Passed to daughter cells during cell division and to future generations

What is signficant about detecting histone modifications REVIEW SLIDE 14

Can be detected through Chromatin immunoprecipitation

What are epigenetic effects of RNA molecules

• X inactivation

• Paramutation in corn

• siRNA molecules that silence genes and transposable elements

• MicroRNAs control expression of genes that produce epigenetic effects

What effect does DNA methylation have on gene expression?

Represses transcription

What effect does Acetylation of histone proteins have on gene expression?

Stimulates transcription

What effect does methylation of histone proteins have on gene expression?

Represses or stimulates transcription depending on which amino acids are methylated

What effect do RNA molecules have on gene expression?

May repress or stimulate transcription

What are stem cells?

undifferentiated cells

What is pluripotency?

Ability to differentiate into any type of cell

What are induced pluripotent stem cells (iPSCs)?

Adult somatic cells forced to dedifferentiate and revert to stem cells; capable of differentiating into many different types of cells

What is X inactivation and how does it occur?

One X chromosome in female cells is permanently silenced; occurs through the action of several genes in the X-inactivation center that encode long noncoding RNAs

Why do the products of X-inactivation interact? REVIEW SLIDE 18

To ensure that one X chromosome is inactive and one remains active in each female cell

What is the role of the Xist gene on the inactive X?

It produces a long noncoding RNA that coats the inactive X chromosome and suppresses transcription

Is Xist on the active or inactive chromosome; what is its role?

Inactive; encodes a IncRNA that coats inactive X chromosome and leads to the silencing of transcription of many genes on the inactive X

Is Jpx on the active or inactive chromosome; what is its role?

Inactive; encodes a IncRNA that stimulates Xist on the inactive X chromosome

Is Tsix on the active or inactive chromosome; what is its role?

Active; Encodes a IncRNA that inhibits transcription of Xist on the active X chromosome

Is Xite on the active or inactive chromosome; what is its role?

Active; Encodes a IncRNA that sustains Tsix expression on the active X chromosome, which inhibits Xist and maintains transcription of genes on the active X chromosome

What is genomic imprinting?

Caused by epigenetic differences in the alleles inherited from male and female parents

What is the imprinting and genetic conflict hypothesis?

Suggests that imprinting evolves because of conflicting evolutionary pressures acting on maternal and paternal alleles

What is the expression of the allele dependent on in genomic imprinting?

It is dependent on whether it is inherited from the male or female parent

What are epigenetic effects in monozygotic twins?

Phenotypic differences between genetically identical monozygotic twins may result from epigenetic effects

REVIEW slides 25 and 26

What is the epigenome?

overall pattern of chromatin modifications possessed by each individual organism

What are ancient epigenomes?

Research reveals that the epigenomes vary among cell types and among ancient hominids