T4 module 4: DNA mutations

Question 1

causes of genetic mutations

Answer 1

• environmental
• spontaneous
• erros in DNA replication

Question 2

why are viruses more prone to mutations?

Answer 2

• RNA backbone more prone to breakage
• no proofreading

Question 3

types of genetic mutations

Answer 3

SOMATIC
- non-germline cells
- not inherited
- earlier mutation happens, the more it spreads
- specific cell tissues

GERMLINE
- germline cells
- can be inherited
- all of offspring’s cells inherit themutation

Question 4

etterberg experiment

Answer 4

showed that mutations were random

• grew bacteria colonies in agar
• replica plating: stamped bacteria onto selective plate with penicillin
• only a few colonies survived
• isolated penicillin resistant colonies in original sample

findings: the mutation for penicillin resistance existed before exposure

Question 5

types of DNA repair

Answer 5

MISMATCH REPAIR
- proofreading from DNAP
or
- mismatch creates kink detected by pr
- cutting enzyme cuts backbone
- another enzyme removes mismatch
- others close gap and repair

NUCLEOTIDE EXCISION REPAIR
- like mismatch repair but for 2+ bases
- damaged bases signal cleavage enzymes
- DNA synth fills gap

BASE EXCISION REPAIR
- uracil mismatch
- DNA uracil glycosylase cleaves U
- AP endonuclease detects gap, cleaves sugar
- other enzymes close gap

Question 6

types of mutations in nucleotide sequence

Answer 6

POINT MUTATIONS: single nucleotide polymorphism

synonymous (silent): doesn’t change AA
nonsynonymous (missense): changes AA (e.g. beta-globin pr-)
nonsense: stop codon
insertions
deletions (e.g. 3 nucleotide deletion in CFTR code - cystic fibrosis)
frameshift: addition/deletion in group of 3

Question 7

types of chromosomal mutations

Answer 7

Deletions
- chromosome fragment lost
- if centromere lost, entire chromosome goes in a few duplications
- in embryos: death/fatal abnormalities

Duplications
- can be advantageous - new gene formed (duplication and divergence, e.g. globin genes)

Inversions
- code breaks off and reattaches in reverse
- no serious consequences

Translocations
- portion of 1 chromosomes attaches to non-homologous one
- usually non coding sections
- offspring may have developmental abnormalities due to nature of chromosome pairing