30. Mutation types and definitions

Question 1

What is a mutation defined as?

Answer 1

An alteration in DNA sequence

Question 2

What are the four categories of mutations?

Answer 2

Germline
Somatic
Spontaneous
Induced

Question 3

How heritable are germline mutations?

Answer 3

• Germline means cells which give rise to egg/sperm so passed onto foetus
• All cells in the offspring carry the mutation genotype but the phenotype is only in cells/tissues expressing the gene

Question 4

To what extent are somatic mutations heritable?

Answer 4

Somatic mutations are not heritable as they only affect somatic cell patches that arise from the original cell

Question 5

How is the time in development that the mutation occurs linked to the size of the mutation patch?

Answer 5

The earlier in development the mutation occurs the bigger the patch

Question 6

What sort of mutations give rise to cancer?

Answer 6

Most mutations in cancer are somatic, affecting a single cell which can form tumours and spread (metastasis)

Question 7

What are spontaneous mutations?

Answer 7

Spontaneous “de novo” mutations can occur at every DNA synthesis stage of cell division

Question 8

How does the size of the gene influence the mutation rate?

Answer 8

If a gene is large it can be more prone to spontaneous mutations

Question 9

What are induced mutations?

Answer 9

They are caused by environmental mutagens

Question 10

What are mutagens?

Answer 10

They are physical or chemical agents that increase the rate of genetic material changes (chemicals, radiation, uv light)

Question 11

What are the four types of chromosomal mutations?

Answer 11

1. Deletion
2. Duplication
3. Inversion
4. Translocation

Question 12

What is the deletion mutation for chromosomes?

Answer 12

The loss of a gene due to a break in the chromosome, deleting the genetic material

Question 13

What is the duplication mutation in a chromosome?

Answer 13

Causes gene dosage effect in which genetic material is duplicated

Question 14

Which 2 types of chromosomal mutations change the amount of genetic material present?

Answer 14

Deletion and duplication change the amount of genetic material

Question 15

What does the inversion mutation involve for chromosomes?

Answer 15

Where there is the rearrangement of genetic material - causing disruption or fusion of genes

Question 16

What does the translocation mutation involve?

Answer 16

Genetic material relocated and joins another chromosome - rearrangement may cause disruption or fusion of genes

Question 17

Which two types of mutations do not change the amount of genetic material?

Answer 17

Inversion and first generation translocation

Question 18

What are the three types of mutations for a single base pair?

Answer 18

Silent
Missense
Nonsense

Question 19

What is a silent mutation?

Answer 19

Where there is no change in the gene product due to the degeneracy of the code and wobble

Question 20

What may a missense mutation cause?

Answer 20

Where there is an amino acid substitution in the gene product due to a change in the first second or third base

Question 21

What is the phenotypic affect of a missense mutation?

Answer 21

Could have very little effect on protein function unless a very important amino acid is lost or the added amino acid changes the 3D protein or binding location

Question 22

What does a nonsense mutation involve?

Answer 22

Premature termination of translation where a stop codon is encoded for instead
- can have a large effect if it occurs early on and large parts of the protein are then missing

Question 23

How may amino acid deletion/insertion mutations have an affect?

Answer 23

• If the insertion/deletion is divisible by three then there could be very little effect on protein function unless a very important amino acid is lost or the added amino acid changes the 3D protein structure
• Frameshift if not divisible by three; depending on how early in the sequence this occurs these mutation often have large effects as they change all subsequent amino acids or lead to premature stop codons