Mutations

Question 1

When do mutations occur?

Answer 1

Gene mutations generally happens when DNA is replicated
Completely random and spontaneous

Question 2

What is the most common type of gene mutations?

Answer 2

Neutral mutations
- sequence of amino acids in the protein is changed but this has no effect on the function of the encoded protein
- tertiary structure or active site of enzyme not affected

Question 3

What are the two different types of gene mutations?

Answer 3

Base deletion
Base substitution

Question 4

What is base deletion?

Answer 4

• a base is lost from the base sequence
• whole base sequence will move back one place (frame shift)
• significant effect - can alter the sequence of all codons following the lost base

Question 5

What is base substitution?

Answer 5

• the ‘wrong’ base is included in the base sequence
• it does not cause frame shift - but might result in a different amino acid being included in the polypeptide chain

Question 6

Advantages of degenerate code

Answer 6

• base substitution can on occasion result in a triplet that still codes for the same amino acid
• sequence of amino acids may not be changed - encoded protein stays the same
• mutation had no effect - silent mutation

Question 7

What are mutagenic agents?

Answer 7

Environmental factors that can increase the rate of mutation

Question 8

Give examples of mutagenic agents

Answer 8

Toxic chemicals e.g. bromine compounds and peroxides
Ionisation radiation e.g. gamma rays and X rays
High energy radiation e.g. UV light

Question 9

What is a polyploidy?

Answer 9

This is when organisms may have 3 or more sets of chromosomes rather than the usual 2 sets

Question 10

What is a non-disjunction event?

Answer 10

The homologous chromosomes do not separate properly during meiosis
Or sister chromatids do not separate properly in 2nd division

Dawn’s syndrome e.g. - trisomy 21