Genetics - Mutations

Question 1

What is a genotype?

Answer 1

Genetic makeup of an individual

Genes or alleles present in an individual

Question 2

What is a phenotype?

Answer 2

Physical appearance of individual

Observable or measurable traits

Question 3

What are point mutations?

Answer 3

Mutations that happen in genes

• Silent
• Frameshift
• Missense
• Nonsense

Question 4

What are gross mutations

Answer 4

Chromosomal mutations

Question 5

What is a silent mutation?

Answer 5

A mutation where there is a change in genes, e.g. a alteration in nucleotide bases, however it does not cause a negative effect and has the same effect as if it hadn’t have occured.

Question 6

Describe a frameshift mutation

Answer 6

• When a base is either deleted or lost, or another base is added to the sequence (insertion or deletion)
• Cause a shift in reading frame which results in an incorrect triplet code and the further reading of the mutated strand changes further codons which changes the overall sequence of amino acid and results in the polypeptide changes
• Usually makes a protein that cannot be used.
• If an insertion of a multiple 3 occurs then another amino acid is added to the polypeptide strand. Reading shift not coded - known as non-frameshift mutation, leads to either fully functional or partially functional protein.

Question 7

What is a missense mutation?

Answer 7

• Single base has been replaced
• Consequence being that the coding for one amino acid is disturbed
• Final protein structure only slightly disrupted

Question 8

What are nonsense mutations

Answer 8

Similar to missense but causes the misplaced bases that causes a triplet code to become a stop codon
The protein becomes truncated and incomplete

Question 9

What can deletions lead to during a gross mutation?

Answer 9

May lead to loss of a complete gene, a section of gene or some of the promoter enhancer elements
Chunk of DNA lost from a chromosome
Can lead to
- Total loss of protein
- Incomplete protein
- Inability to activate transcription properly

Question 10

Describe base excision repair. Use the example of cytosine

Answer 10

1. Cytosine can easily lose an amino group (during damage) forming a base called uracil which cannot form guanine
2. Glycosylase discovers the defect and removes the base uracil
3. More enzymes remove the rest of the nucleotide from the strand
4. DNA polymerase fills the gap and DNA strand is sealed by DNA ligase

Question 11

Describe the process of nucleotide excision repair

Answer 11

1. Damage or injuries can cause 2 nucleotides to bind incorrectly
2. The enzyme exinuclease finds the damage and cuts the DNA strand removing 12 nucleotides
3. DNA polymerase fills the gap
4. DNA ligase seals the DNA strand

Question 12

What is a mutation?

Answer 12

Sudden, abrupt and random changes in genetic material (DNA or RNA) of organisms