Genetics Exam 3

The inactivation of an X chromosome occurs in ______

female mammals

Before replication, a heterochromatic region has sites with fully methylated DNA and nucleosomes with H3K9me3 histone modifications. After DNA replication, what would be the constituents of each daughter chromatid?

hemimetylated DNA half of the H3 histones with H3K9me3 modifications

Which modification is commonly found for lysines in histones associated with constitutive heterochromatin?

hypoacetylation

cis-epigenetic change

maintained only at a given site and does not affect the expression of a gene elsewhere in the nucleus.

The methylation of hemimethylated sites is called ______

maintenance methylation

An RNA that does not encode a polypeptide is a(n) ______ RNA

nc - noncoding

The basic repeating unit of chromatin is the _________ composed of________ wrapped around an octamer of __________ proteins

nucleosome DNA (147bp) histones

Trans-epigenetic mechanisms are more commonly found in ______

prokaryotes single-celled eukaryotes

Regions of a protein that control the binding of particular proteins to nucleosomes with posttranslational modifications (PTMs) are called ______ domains.

reader

When bound to a nucleosome carrying a modified histone, a binding protein with a reader domain but no writer domain will ________

recruit chromatin-modifying enzymes

When sites containing transposable elements (TEs) are converted to heterochromatin, the TEs are prevented from moving because the genes for transposition are ______.

silenced

The Igf2 gene will be expressed if ______

the ICR and DMR are methylated the Igf2 gene can be stimulated by the enhancer

3 examples of how environmental factors may function as epigenetic regulators?

toxins diet temperature

Activation of a gene that encodes a transcription factor capable of stimulating its own expression and/or the expression of other genes is an example of a ______ mechanism.

trans-epigenetic

Regions of a protein that catalyze the addition of posttranslational modifications (PTMs) are called _________

writer domains

Match the type of chromatin structure with the stage of the cell cycle in which it would be observed. 1)Interphase 2)M phase 3)M phase through interphase in two daughter cells

1-Most chromosomal regions are composed of euchromatin. 2-Euchromatic regions condense into constitutive and facultative heterochromatin. 3-Constitutive and facultative heterochromatin regions retain the same pattern observed in mother cell.

A heterochromatic region with fully methylated DNA and extensively modified histone H3 prior to DNA replication, will have ______ (the) levels of these modifications in the daughter chromatids produced after DNA replication.

1/2

The role of heterochromatin in repressing transcription may be due to interference with which factors?

Coactivators General transcription factors Transcriptional activators

features associated with constitutive heterochromatin in yeast and animal cells

Composed of many, short tandemly repeated sequences DNA is highly methylated on cytosines Trimethylation of a lysine at the ninth position in histone H3 Located at telomeres and close to centromeres

What accounts for the molecular mechanism of imprinting of the Igf2 gene?

Differential methylation during oogenesis and spermatogenesis

changes that can occur during embryonic development that will lead to a pattern of differential gene expression unique to a specific cell type.

Epigenetic changes that enable specific genes to be transcribed Epigenetic changes that cause specific genes to be permanently repressed

True or false: Gene regulation may be related to epigenetic events such as the binding of transcription factors to certain genes, which induce permanent mutations in the DNA.

False

3 examples of how programmed changes during development may function as epigenetic regulators?

Genomic imprinting X-chromosome inactivation Cell differentiation

Which changes occur following the binding of Xist RNAs to the Xi?

Histone variant macroH2A is incorporated into the nucleosomes along the Xi Recruitment of protein complexes to Xi Covalent modification of specific sites in histone tails Recruitment of DNA methyltransferases to Xi

diseases that have been associated with abnormalities in heterochromatin formation.

ICF syndrome Roberts syndrome

How does heterochromatin prevent the proliferation of viruses?

Inhibiting the expression of viral genes needed to produce new viruses

ways that heterochromatin can inhibit transcription.

Inhibiting the recruitment of general transcription factors or coactivators Preventing activators from binding to enhancer sequences

4 examples of epigenetics?

Localization of histone variants Covalent histone modification DNA methylation Chromatin remodeling

Characteristics of heterochromatin

Localized along the periphery of the cell nucleus Highly compact structure Inhibition of gene expression

features associated with facultative heterochromatin?

Methylation at CpG islands located in the regulatory regions of genes Trimethylation of histone H3 at the 9th or 27th lysine Located at multiple discrete sites between the centromere and telomeres In animals, contain LINE-type repeated sequences

Which of the following is an example of epigenetic inheritance? Mutation of DNA in a sperm cell Modified histone of a stem cell Methylation of DNA that occurs in an oocyte chromatin modification that causes cancer in a lung cell

Methylation of DNA that occurs in an oocyte

2 characteristics of euchromatin

Occupies a central position in the nucleus High level of gene expression

steps of how a gene may be targeted for silencing by PcG complexes

PRE-binding proteins to PRE and recruits PRC2 PRC2 catalyzes trimethylation Transcription is inhibited

mechanisms responsible for reestablishing heterochromatin structure after DNA replication.

Presence of higher-order heterochromatin structure Trimethylation of histones DNA methylation

3 key functional roles for heterochromatin in eukaryotic cells?

Preventing viral proliferation Silencing genes Preventing movement of transposable elements

In the prevention of viral proliferation, what affect does heterochromatin have on a virus that has integrated into the host genome as proviral DNA?

Prevents expression of proviral genes needed to produce new viruses

How does heterochromatin prevent the movement of transposable elements (TEs)

Silencing genes needed for transposition

How do transcription factors contribute to epigenetic modification?

Transcription factors recruit chromatin modifying proteins, such as DNA methyltransferase.

Which of the following are true regarding epigenetics?

Variations are reversible from one generation to the next Epigenetic changes are transmissible from cell to cell Variations of gene expression are unrelated to variations in the DNA base sequence Epigenetic changes may be transmitted to offspring

which processes are prevented by heterochromatin formation in eukaryotic cells

Viral proliferation Transcription Transposable element movement

statements regarding X inactivation

When the Xist gene is inactive the X chromosome is active In very early embryos, both X chromosomes are active Expression of Tsix from both X chromosomes inhibits the expression of Xist

In mammals, females (XX) and males (XY) express genes on the X chromosome at the same levels because of ______.

X chromosome inactivation

List the events of X-chromosome inactivation in the correct sequence. putting the first event at the top.

X chromosomes pair at tsix gene pluripotency factors shift to one X tsix gene without pluripotent factors is inhibited xist recruits proteins

Which two areas of the X chromosome play a key role in X inactivation?

Xist Tsix

What happens when pluripotency factors stimulate the expression of Tsix?

Xist is inhibited.

Abnormalities in heterochromatin formation have resulted from loss-of function mutations affecting the activity of which enzymes?

acetyltransferase DNA methyltransferase

Once bound to a nucleosome carrying a modified histone, a binding protein with both a reader and writer domain will _____

catalyze a posttranslational modification

Genomic imprinting and X-chromosome inactivation are examples of ______ mechanisms that occur during development.

cis-epigenetic

Hypoacetylation of lysines in histone tails is a common modification found in

constituitive heterochromatin

Regions of the chromatin containing numerous, short, tandemly repeated sequences that are located near the centromeres and at the telomeres of eukaryotic chromosomes are called ______ heterochromatin

constitutive

During cell division, from M phase in the mother cell to interphase in the resulting two daughter cells, a chromosome will usually retain the same pattern of _______ and __________heterochromatin that was found in the mother cell.

constitutive facultative

The methylation of a previously unmethylated site is called ______

de novo methylation

X chromosome inactivation occurs where and when

during embryogenesis in females.

X-chromosome inactivation is an epigenetic event that occurs during ______

embryogenesis

DNA methylation, chromatin remodeling, covalent histone modification, and localization of histone variants are all examples of molecular mechanisms that are involved in

epigenetics

The variation of gene expression that is not related to the variation of the DNA, is transmissible, and is reversible is described as

epigenetics

Heterochromatic regions found at multiple discrete sites located between the centromeres and telomeres, and which contain methylated DNA at CpG islands in regulatory regions, are called ______ heterochromatin.

facultative

Heterochromatic regions that are cell-specific and silence genes that should not be expressed in a certain cell type are called __________

facultative heterochromatin

Regions of heterochromatin that vary among different cell types are called

facultative heterochromatin

True or false: Because epigenetics refers to heritable changes in gene expression, all epigenetic changes are examples of transgenerational epigenetic inheritance.

false