Question 1

With respect to X-chromosome inactivation, which, if any, of the following statements are not correct ?

Accepted Answer

A)  X-chromosome inactivation in mammals begins in the pre-implantation embryo 
B)  In humans all diploid cells that carry two normal X-chromosomes are subject to a random pattern of X-inactivation. 
C)  Once a decision has been made to inactivate an X chromosome (either the paternal or maternal X), all descendant cells show the same pattern of X-inactivation. 
D)  The inactivated X chromosome becomes a highly condensed Barr body in which genes are silenced across the length of the chromosome.

Question 2

In Beckwith-Wiedemann syndrome an allele that is normally epigenetically silenced is somehow expressed, resulting in biallelic expression. Illustrate how the expression of relevant genes is altered to cause the disease.

Accepted Answer

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Question 3

The nuclear genome in our cells makes four types of RNA polymerase, a simple RNA polymerase that is imported into mitochondria and is dedicated to transcribing mitochondrial DNA plus three types of multi-subunit RNA polymerase that transcribe nuclear DNA sequences. What types of DNA sequence are transcribed by the different nuclear RNA polymerases.

Accepted Answer

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Question 4

Splice junction sequences show a certain degree of sequence conservation. Give consensus sequences for the splice donor and splice acceptor sequences.

Accepted Answer

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Question 5

How does uniparental diploidy occur in humans, and what are the consequences?

Accepted Answer

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Question 6

With respect to CpG islands in our genomic DNA, which, if any, of the following descriptions do not apply?

Accepted Answer

A)  frequently occurring (there are about 30,000 in the human genome). 
B)  long DNA sequences (typically from 10 kb to 100 kb in length). 
C)  low CG dinucleotide frequency. 
D)  frequently associated with transcriptional start sites.

Question 7

Outline the major global changes in DNA methylation that occur during mammalian gametogenesis and early embryonic development.

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Question 8

Match individual variant histones i) to iv) to one or more of the possible functions listed in
a) to
g).

Accepted Answer

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Question 9

With respect to epimutations, which, if any, of the following statements, is false, from a practical viewpoint?

Accepted Answer

A)  The term epimutation means an unexpected change in chromatin conformation, causing a gene to be expressed in an abnormal way that is not related to its base sequence. 
B)  A primary epimutation is a change in chromatin confirmation that is not related directly to any change in the base sequence. 
C)  A secondary epimutation arises from a standard mutation that results in a profound change of expression in a gene that regulates chromatin conformation. 
D)  A "chromatin disease" is a disorder that is consistently caused by a primary epimutation.

Question 10

With reference to imprinting disorders, which, if any, of the following statements is false?

Accepted Answer

A)  About one quarter of individuals with Angelman syndrome lack a paternal chromosome 15. 
B)  With the exception of abnormal chromosome segregation, imprinting disorders always result from a deletion or inactivating mutation within, or spanning the imprinted gene cluster. 
C)  In some imprinting disorders, disease results from inappropriate biallelic expression of a gene. 
D)  Angelman and Prader-Willi syndrome are very different disorders but can be caused by precisely the same large deletion at 15q11-q13.

Question 11

Which, if any, of the following descriptions is false?

Accepted Answer

A)  Genomic imprinting in mammals really means that a very few genes are expressed from one allele only, according to the sex of the parent. 
B)  Imprinted genes are often found in clusters of genes, many of which are imprinted. 
C)  means that in a diploid cell two copies of the same chromosome are inherited from one parent 
D)  Within an imprinted gene cluster, all genes on one of the two parental chromosomes are silenced, but the equivalent genes on the other parental chromosome are not subject to silencing.

Question 12

In some imprinting disorders the normal allele of an imprinted gene locus is inactivated (so that both alleles are silenced). Illustrate how this happens in Angelman and Prader-Willi syndromes.

Accepted Answer

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Question 13

Rett syndrome is a classic chromatin disease. What is meant by a chromatin disease and what are the characteristics of Rett disease?

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Question 14

With respect to microRNAs, which, if any, of the following statements, is true?

Accepted Answer

A)  MicroRNA genes often occur in gene clusters within introns of protein-coding genes and are usually transcribed by RNA polymerase II. 
B)  Like an mRNA a miRNA is initially produced as a larger precursor RNA that, like the great majority of mRNAs, usually has a 5' cap and a poly(
A)  tail. 
C)  MicroRNAs are produced by germ-line cells only. 
D)  An miRNA is initially produced as a duplex RNA but in order to work it needs to be converted into a single-strand RNA.

Question 15

What are the principal functions of DNA methylation in mammalian cells?

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Question 16

DNA methylation is one epigenetic mechanism where it is easy to appreciate how the pattern of epigenetic settings is stably inherited from one cell generation to the next. What are the features of the DNA methylation mechanism that suggest this?

Accepted Answer

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Question 17

A classical position effect means that a gene can be partly or fully silenced simply if it is moved to a different chromosomal location. Explain how this happens.

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Question 18

According to the manner in which they work, three main classes of proteins that modify chromatin are recognized. What are these three classes and explain, with examples, what distinguishes the individual classes.

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Question 19

Which, if any, of the following statements is incorrect?

Accepted Answer

A)  In X-chromosome inactivation the inactivated X chromosome is epigenetically silenced by a transcript, the XIST RNA, that is produced from the active X chromosome. 
B)  The XIST RNA works by coating most of the X chromosome that is to be inactivated and then recruiting Polycomb proteins to condense the chromosome. 
C)  The inactivated X chromosome carries the kinds of histone modification that are typical of heterochromatin. 
D)  The pattern of X-chromosome inactivation is made randomly but once it has been established the same pattern of X-inactivation is propagated through all mitotic and meiotic cell divisions.

Exam 6: Principles of Gene Regulation and Epigenetics