Mutations

Question 1

What are the two definition of a mutation?

Answer 1

A hero table alteration in a gene or chromosome (a change in the sequence of nucleotides)
OR
The process that produces the alteration (the source of most alleles)

Question 2

Give examples of exogenous mutagens and how this leads to mutations

Answer 2

Ionising radiations / particles,
Free radicals,
Mutagenic chemicals,
Anti-cancer agents.

These lead to defective or error-prone DNA repair which leads to a mutation.

Question 3

What percentage of ionising radiation is natural and what is artificial?

Answer 3

16% of ionising radiation is artificial (15% of this is medical)
84 p% of ionising radiation is natural (50% is from radon gas in the ground)

Question 4

Give examples of endogenous mutagens and how this leads to mutations

Answer 4

DNA replication defects,
Transposable elements.

These lead to defective or error-prone DNA repair which leads to a mutation.

Question 5

What are transposable elements? (7)

Answer 5

• It is a specific DNA sequence (larger than a gene)
• Supernumerary (many copies)
• Always contained within other DNA molecules; never in a free form
• Move (transpose) as a discrete unit
• Move (transpose) to random sites
• Insertionally inactivate target gene
• Ubiquitous (found everywhere)

Question 6

What three different effects can transposable elements have on proteins?

Answer 6

• Make the protein not functional (eg transpose in middle of protein)
• Activate transcription in other cell types (eg if transposed into initiation sequences)
• No effect at all (if transposed to introns where it is spliced out)

Question 7

Name the type of DNA changes that result in a single nucleotide change.

Answer 7

Deletion
Insertions
Substitution

Question 8

Name the four different effects that single nucleotide changes can have

Answer 8

• Change the gene product,
• Change the amount if gene product,
• Change the polypeptide length,
• No effect.

Question 9

What are the two different ways a single nucleotide change can be classified depending on the type of base it changes to?

Answer 9

TRANSITION - when the base changes to the same type of base. Eg a purine to purine (A to G) or a pyrimidine to pyrimidine (T to C)

TRANSVERSION - When the base changes to a different type of base eg purine to pyrimidine or visa versa (A/G to C/T)

Question 10

What is a missense?

Answer 10

A missense mutation is a single nucleotide change that changes the gene product / amino acid

Question 11

What is another term for a synonymous mutation and what is it?

Answer 11

A synonymous mutation is one that is silent or neutral this means that they are mutations that do not have an effect.

Question 12

Name the three types of mutation that can cause a change in polypeptide length.

Answer 12

Frameshift mutations (insertions or deletions)
Mutations of stop codons (translation continues)
Nonsense mutations (a codon is changed into a stop codon to stop translation prematurely)

Question 13

Name the types of mutation that can change the amount of gene product.

Answer 13

Mutations affecting transcription or translation affect the amount of gene product. Eg 
Alter promoter activity,
Alter translation initiation at AUG ,
Prevent mRNA splicing,
Reduce mRNA stability.

Question 14

Name the six types of chromosomal mutation

Answer 14

Deletion 
Insertion 
Inversion 
Translocation 
Duplication 
Substitution

Question 15

What causes a chromosomal mutation?

Answer 15

A double stranded break which could not be repaired by normal mechanisms.

Question 16

What is Robertsonian translocation?

Answer 16

A rare form of chromosomal arrangement when two chromosomes break at the centromere and the two Q (long) arms fuse (centric fusion) to form one, large chromosome. The p arms from acentric fragments.

Question 17

What is the Philadelphia chromosome?

Answer 17

This is when chromosome 9 and 22 undergo reciprocal translocation (exchange of genetic material between two non homologous chromosomes). This creates a fusion gene called BCR-ABL1 on chromosome 22which codes for a hybrid protein that causes the cell to divide uncontrollable.
This leads to Leukaemia, particularly myeloid Leukaemia.