Genes and other genomic elements

Question 1

In vertebrates up to 10% of the DNA cytosine residues are ?

Answer 1

Methylated

Question 2

Methylation is restricted to ?

Answer 2

Cytosine residues immediately 5’ of Guanosine residues (ie CpG)

Question 3

CpG dimers are actually quite rare in ?

Answer 3

The vertebrate genome

Question 4

What is maintenance methylation ?

Answer 4

Methyl groups are added to newly synthesised DNA opposite methylated groups on the parent strand

Question 5

What is De novo methylation?

Answer 5

This a process by which methyl groups are added to unmethylated DNA at specific CpG sites

Question 6

What does methylation result in ?

Answer 6

Repression of gene activity, ie transcription is inhibited if the DNA is methylated

Question 7

What is the mechanism involve for methylation ?

Answer 7

Mechanism involves methyl-CpG-binding proteins that recruit histone deacetylases that in turn result in tight packaging of the chromatin and silencing of the genes

Question 8

Actively transcribed genes can be identified by ?

Answer 8

The presence of CpG islands – higher than expected frequency of unmethylated CpG

Question 9

How can actively transcribed genes also be identified by ?

Answer 9

Can be recognised by enzymes that cut methylated, but not non-methylated DNA (or vice versa)

Question 10

What does methylation affect?

Answer 10

Imprinting, X-chromosome inactivation and defects in the process can cause diseases such as ICF and some cancers.

Question 11

Explain Conventional pseudogenes ?

Answer 11

Where mutations have occurred in a gene sequence and caused it to become non-functional. More mutations will accumulate in the sequence until it is barely recognisable as a gene

Question 12

Explain Processed pseudogene ?

Answer 12

A gene sequences that contains neither introns or promoters. These are derived from DNA copies of mRNA which have become incorporated into the genome.

Question 13

What do Gene Fragments do?

Answer 13

Sequences in the genome that resemble incomplete sections of genes

Question 14

Explain fully what a Microsatellite repeat is ?

Answer 14

Microsatellite repeats are very common in the human genome and are caused by replication slippage. This is where the template and daughter strands become misaligned during replication and repeats are either added or deleted

Question 15

Explain a little bit about The Prosecutor’s Fallacy ?

Answer 15

• DNA profiling might suggest that the probability of finding an identical match to a crime scene sample is 0.00001 ie 1 in 100,000
• If the probability of a match is 1 in 10000 and all the people in a large town of 20000 people are tested then there is a high likelihood of a random match (>85%). Thus there is no overwhelming reason to believe that a person with a matching profile is guilty. Yet the prosecutor might try to persuade the jury that it was very unlikely ie a 0.0001% (1/10000) chance of a match.