Topic 4---B: Diversity and selection- 2. mutations

Question 1

What is a gene mutation?

Answer 1

They involve a change in the DNA base sequence
(which could lead to a change in amino acid sequence of the polypeptide which can alter the function of a protein)

Question 2

Substitution

Answer 2

One base is substituted with another- Changes the polypeptide (mis-sense mutation) may/ may not alter the protein function

Question 3

Deletion or addition

Answer 3

1 base is deleted or one is added
After deletion or addition the first base of the next triplet becomes the last base of the preceding triplet (frameshift mutation)
It will change the number of bases present

Question 4

Effect of mutations (degenerate)

Answer 4

• Some amino acids are coded for by more than 1 triplet so not all substitution mutations will result to a change in amino acid sequence of the protein. (silent mutation)

Question 5

Non-sense mutation

Answer 5

Base substitution resulting in the formation of 1 of the 3 stop codons resulting in a premature termination of a polypeptide

Question 6

How can mutations occur?

Answer 6

When DNA is misread during replication

Question 7

What can cause an increase in the rate of mutations?

Answer 7

Mutagenic agents
- Ultraviolet radiation
- Ionising radiation

Question 8

Chromosome mutation

Answer 8

• Lead to inherited conditions
• Occurs due to a fault in meiosis

Question 9

Down syndrome

Answer 9

• Caused by a person having an extra copy of chromosome 21
• Non-disjunction means that chromosome 21 fails to separate properly during meiosis so one cell gets an extra copy of 21 and another gets none.