MBG: BLOCK 2: TOPIC 7: PRINCIPLES AND PROPERTIES OF EPIGENETICS

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Questions and Answers

What is the primary outcome of X-inactivation in females?

Increased transcription of X-linked genes

Reduction of chromosomal abnormalities

Dosage compensation of X-linked gene expression (correct)

Complete silencing of one X chromosome in all cells

Mosaicism refers to what phenomenon in genetic expression?

Uniform expression of genes across all cells

The presence of different genotypes in an organism's cells (correct)

The ability of an organism to adapt to environmental changes

The complete absence of genetic variations in an organism

How does DNA methylation influence chromatin structure?

By triggering the condensation of heterochromatin and gene repression (correct)

By enhancing the replication of chromatin

By promoting euchromatin formation and transcription

By completely erasing gene expression sites

What defines facultative heterochromatin?

It remains in a condensed state until needed. Signup and view all the answers

What is one consequence of X-inactivation in terms of gene dosage?

It allows equal gene dosage of X-linked genes between males and females. Signup and view all the answers

What role do mRNA molecules play in epigenetic regulation?

They can influence gene expression without altering the DNA sequence. Signup and view all the answers

What is the role of mRNA in the process of X-inactivation?

It assists in the recruitment of proteins necessary for chromatin inactivation. Signup and view all the answers

What is the primary effect of lyonization on genetic expression?

It allows for random inactivation of either maternal or paternal X chromosome. Signup and view all the answers

What is a consequence of X-inactivation on gene expression in females?

It leads to equal dosage of X-linked genes in males and females. Signup and view all the answers

Mosaicism is best defined as:

The presence of two or more genetically different cell lines within a single organism. Signup and view all the answers

Which characteristic is associated with euchromatin?

Loosely coiled and actively undergoing transcription Signup and view all the answers

What mechanism does dosage compensation utilize to balance gene expression between males and females?

Complete silencing of one X chromosome in females. Signup and view all the answers

Which of the following describes the process of chromatin remodeling?

It changes the structure of chromatin to regulate gene expression. Signup and view all the answers

DNA and histone methylation differ primarily in which aspect?

Both processes lead to gene silencing but occur on different substrates. Signup and view all the answers

The major difference between constitutive and facultative heterochromatin is:

Constitutive heterochromatin is always transcriptionally silent, while facultative can be active. Signup and view all the answers

What is the primary function of histone methyltransferases?

To add methyl groups to specific histone residues. Signup and view all the answers

What is the main function of histone methyltransferases in the methylation process?

To add methyl groups to specific histone residues Signup and view all the answers

How do chromatin-remodeling complexes (CRCs) utilize energy?

By deriving energy from ATP Signup and view all the answers

Which of the following best describes facultative heterochromatin?

Silenced euchromatin that can be reactivated Signup and view all the answers

What characterizes constitutive heterochromatin?

It plays critical structural roles but is never transcribed Signup and view all the answers

What impact does chromatin remodeling have on gene expression?

It can shift associated material in nucleosomes influencing gene expression Signup and view all the answers

What role does heterochromatin play in chromosomal protection during cell division?

It protects against chromosomal changes and aids in alignment Signup and view all the answers

Which of the following processes causes silencing of genes in facultative heterochromatin?

Deactivation through changes in methylation Signup and view all the answers

How has the role of heterochromatin changed in scientific understanding?

It is now recognized for its structural and functional importance. Signup and view all the answers

Which histone modification is associated with facultative heterochromatin?

Mono and Dimethylated H3-Lys9 Signup and view all the answers

What percentage of the human genome is made up of constitutive heterochromatin?

15-20% Signup and view all the answers

Study Notes

Epigenetics

The study of how heritable traits are modified by environmental influences or other mechanisms without changing the DNA sequence

Euchromatin

Loosely coiled during interphase
Condensed during mitosis
Often undergoing active transcription
Light bands in G-banding

Heterochromatin

Tightly coiled
Remains condensed from prophase through mitosis
Not transcriptionally active
Dark bands in G-banding
Late replicating and inaccessible to the replication machinery
Can be constitutive or facultative

Constitutive Heterochromatin

Never transcribed
Found in regions that are never transcribed
Plays critical structural roles

Facultative Heterochromatin

Can be silenced or activated
Regions become heterochromatic in specific cell types or tissues

DNA Methylation

Addition of a methyl group to cytosine or adenine bases
Associated with heterochromatin formation and repression of gene expression
Important process in epigenetics and genetic disease

Importance of Heterochromatin

Originally believed to be "junk" DNA
Plays structural and functional roles
Confers strength and protection to centromeres
May protect against changes in sequence and can prevent crossing over
May aid in alignment and separation of chromosomes during mitosis and meiosis
Heterochromatic regions of the Y-chromosome contain fertility factors
Permanently turn off genes that were used in development and are no longer needed
Plays a role in cellular specialization and differentiation

Chromatin Remodeling

Molecular mechanism frequently involves repositioning, acetylation, methylation, and/or replacement of histone variants
Several different multi-protein complexes, known as chromatin-remodeling complexes (CRCs), can restructure chromatin to increase or decrease transcription
CRCs use energy derived from ATP to initiate changes
CRCs can disrupt nucleosome structure without displacing them or reposition them to make key DNA-binding sites accessible

Histone Methylation

Histone methyltransferases add methyl groups to specific histone resides
Correlates with changes in heterochromatin and euchromatin
Methylation can be used to silence or activate transcription

Lyonization/X-Inactivation

Inactivation of genes on the X chromosome that exhibit dosage effects

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Description

Explore the fascinating world of epigenetics and chromatin structure in this quiz. Learn about euchromatin, heterochromatin, and the roles of DNA methylation. Delve into how these mechanisms affect gene expression and cellular functions.