Mutation

Question 1

What is the defintion of a mutation?

Answer 1

Any alteration to the genetic material that produces a heritable change in the nucleotide sequence

Question 2

What can people associate with ‘mutation’ but isn’t?

Answer 2

• Chemical damage to DNA that is not inherited or chemical moderations of nucleotides associated with temporary changes in gene function
• Genetic recombination: A process that re-assorts alleles between homologous chromosome pairs?

Question 3

When does homologous recombination actually take place?

Answer 3

• During gametogenesis (formation of gametes)

- Double-strand break

Question 4

What can happen if homologous recombination goes wrong?

Answer 4

Large scale aberrations

-can cause an incorrect chromosome number and breakages which may be rejoined in the wrong configurations

Question 5

What are the types of large-scale change (global) mutations? and their subdivisions?

Answer 5

1) Chromosomal aberrations:
- Deletions
- Duplications
- Insertions
- Inversions

2) Genome rearrangements (arise from chromosomal breakage and ause re-distribution of genetic material between different chromosomes

3) Changes in chromosome number (Downes syndrome)
- usually arise from mistakes in chromosome segregation at cell division

Question 6

What are the types of localised change mutations? and their subdivisions?

Answer 6

1) Point mutations (single nucleotide changes)
- Base substitution
- Loss or gain of a single nucleotide

2) Deletion/Insertion
- loss/gain of 2 or more bases

3) Duplication
- a sequence is repeated

4) Inversion
- a sequence is inverted

5) Transposition
- movement of a piece of DNA from one location to another

Question 7

What are the groups of the majore bases of nucleic acids?

Answer 7

Purine - Guanine, Adenine

Pyrimidine - Cytosine, Thymine, Uracil

Question 8

What is the definition of a transition mutation?

Answer 8

Changes a purine for a purine or a pyrimidine for a pyrimidine

Question 9

What is the definition of a transversion mutation?

Answer 9

Changes a purine for a pyrimidine or a pyrimidine for a purine

Question 10

How can point mutations be classified?

Answer 10

• Silent, missence or nonsense

- frameshift due to insertion/deletion

Question 11

What triplet code is the stop codon?

Answer 11

UGA

Uracil, Guanine, Adenine

Question 12

What are the effects of points mutations on the protein?

Answer 12

• No effect in Samesense (DNA polymorphism) and missense (Protein polymorphism)
• Change of function in missense and small deletions
• loss of function in missense, nonsense and frameshifts

Question 13

What are the effects of point mutations on the organism?

Answer 13

Could range from:

• no effect
• loss of function
• altered phenotype
• genetic disease

Question 14

How does the mutation affect diploids (two copies of each chromosome) ?

Answer 14

• Mutation prevents gene product synthesis
• Alters gene product
• A MUTATION IN AN ESSENTIAL GENE MAY BE MASKED

Question 15

How does the mutation affect haploids? (yeast and bacteria)

Answer 15

• mutation that affects gene function usually alters the phenotype
• A MUTATION IN AN ESSENTIAL GENE IS LETHAL

Question 16

What are the three phenotypes depending on the activity of the protein?

Answer 16

1) Wild type (little or no activity and half the wild-type protein is enough eg, mutation is recessive)
2) Mutant (mutant protein alters function that displaces the wild type protein eg, mutation is dominant)
3) Intermediate (if both wild-type and mutant proteins function but differently eg, the mutation is codominant

Question 17

When do recessive mutations reveal themselves?

Answer 17

When sexual reproduction combines two mutant alleles

-eg, cystic fibrosis (1/25 people carry the mutant gene)

Question 18

What is a reversion?

Answer 18

The same process that causes a point mutation can also be responsible for reversing it at the same site