Unit 3 - Ch. 19: Gene Mutation And Repair

Question 1

What is a gene mutation?

Answer 1

A heritable change in the DNA sequence of a gene
- can be beneficial, neutral, it harmful
- provide allelic variation

Question 2

What are the three types of point mutations?

Answer 2

Silent: No change in amino acid
Missense: Changes in amino acid
Nonsense: Change of amino acid to STOP coding

Question 3

Which point mutation type is most harmful?

Answer 3

Nonsense, because it creates a premature stop codon.

Question 4

What is a frameshift mutation?

Answer 4

A mutation caused by an insertion/deletion not in multiples of 3, changing the reading frame

Question 5

What’s the difference between somatic and germline mutations?

Answer 5

Germline (on gametes) = heritable; Somatic (in body cells)= not passed on

Question 6

What is direct repair?

Answer 6

Enzyme directly reverses the damage (e.g., photolyase splits thymine dimers)

Question 7

What is base excision repair (BER)?

Answer 7

Fixes small, non-bulky errors using glycosylase and DNA polymerase

Question 8

What is nucleotide excision repair (NER)?

Answer 8

Fixes bulky distortions (e.g., thymine dimers); defective in Xeroderma Pigmentosum.

Question 9

What is mismatch repair?

Answer 9

Corrects replication errors missed by DNA polymerase proofreading.

Question 10

What are the two methods for double-strand break repair?

Answer 10

HRR (accurate): uses sister chromatid as template
NHEJ (quick, error-prone): joins ends directly when there is no template