6.1.1 Gene Mutations

Question 1

What is a genetic mutation?

Answer 1

• A change in the sequence of base pairs in a DNA molecule, potentially resulting in an altered polypeptide

Question 1

About mutations :

Answer 1

• Continuously occur
• Spontaneously occur
• During DNA replication

Question 2

What is a mutagen?

Answer 2

• A factor increasing the frequency of mutations

Question 3

What are some examples of mutagens?

Answer 3

• Ionising radiation (X-Rays, breaking strands causing them to be repaired which is when mutations can occur)
• Deaminating chemicals (alter chemical structure of bases)
• Methyl or ethyl groups (added to bases, leading to incorrect base pairing)
• Viruses can insert sections of viral DNA into DNA of cells

Question 4

What does the DNA code being degenerate mean?

Answer 4

• Several triplets code for the same amino acid
• So most mutations do not alter polypeptide, or only alter it slightly so the structure and function of the protein is not changed
• Mutations can occur in non-coding parts of DNA too so no effect on the amino acid sequence at all

Question 5

3 Types of mutation

Answer 5

• Insertion
• Deletion
• Substitution

Question 6

Insertion of nucleotides

Answer 6

• When a new base is inserted into DNA sequence
• Changes amino acid that would have been coded by the original base triplet
• Knock on effect by altering triplets further on in DNA sequence
• ‘Frameshift mutation’
• Affects structure of polypeptide, and so affects its function

Question 7

Deletion of Nucleotides

Answer 7

• When a base is deleted
• CHanges amino acid
• And knock on effect
  #- Etc

Question 8

Substitution

Answer 8

• Only changes that triplet
• Can be silent (degenerate code etc)
• Can be a missense mutation (alters 1 amino acid in the protein (sickle cell anemia))
• Can be nonsense (creates a premature stop codon, causing polypeptide chain produced to be incomplete and affects final protein structure and function. Cystic fibrosis example)

Question 9

Beneficial mutations

Answer 9

• Benefit
• Skib colour
• Protection from UV, still absorbs vitamin D

Question 10

Harmful mutatuons

Answer 10

• Sickle cell anaemia
• Cystic fibrosis

Question 11

Neutral

Answer 11

• Doesnt alter
• Barely alters
• Alters, performs different function but no adv or disadv
• Eg. Bitter taste in burssel sprouts
• Could have been useful back in the day
• Mutated allele
• Not advantageous because chemical in brussel sprout is not toxic
• Neutral mutation to taste it