Mutations

Question 1

When do mutations normally occur

Answer 1

Interphase during DNA replication

Can also happen during mitosis and meiosis

Question 2

Steps of DNA replication

Answer 2

Initiation
Elongation
Termination

Question 3

Describe initiation in DNA replication

Answer 3

DNA helicase unwinds double helix

Breaks hydrogen bonds between complimentary bases

Question 4

Describe elongation in DNA replication

Answer 4

RNA primers = starting point for leading strand
Grows one base at a time
DNA polymerase is key enzyme. Adds complimentary bases

Question 5

Describe termination in DNA replication

Answer 5

• RNA primers removed via DNA exonuclease
• Gaps closed with DNA polymerase adding complimentary nucleotides
• DNA ligase adds phosphate in remaining gaps = backbone
• nuclear enzymes proofread structure and remove misspaired bases

Question 6

Mitosis vs meiosis

Answer 6

Mitosis = 2 diploid daughter cells. Genetically identical to parental 
Meiosis = haploid gametes from diploid germline cells

Question 7

Transition =

Answer 7

Mutations between purines
A and G
Mutations between pyrimidines
T and C

Question 8

Trans versions =

Answer 8

Mutations from purines to pyrimidines or vice versa

Question 9

Different types of gene mutations

Answer 9

Point 
- Silent 
- Missense (change AA function) 
- Nonsense (early stop codon)
Frameshift
- substitution 
- insertion 
- deletion

Question 10

Different types of chromosme mutations

Answer 10

Frameshift

• deletion
• duplication
• inversion
• translocation

Question 11

Sickle cell disease

Answer 11

• people of African/Caribbean origin most affected
• unusual RBC shape
• cells stick in blood vessels
• serious and lifelong
• treatment manages problems
• heterozygote = malaria resistant

Question 12

E.g. point mutation

Answer 12

Colourblindness
On X chromosome = affects more males
Mostly red/green

Question 13

E.g. frameshift mutation

Answer 13

• Tay Sachs disease
• autosomal recessive
• nerve cells destroyed in brain and spinal cord = loss of motor control and seizures
  Death around 4 years old

Question 14

Typical genome difference between people

Answer 14

~20 mil bp
0.6% total number bp in genome
= average 60 new mutations compared to parents