Gene Propagation (Exam 3)

Question 1

What are double strand breaks?

Answer 1

when the sugar phosphate backbone is broken in both strands

Question 2

What types of damage can occur after double strand breaks have occurred?

Answer 2

nucleotide deletions
apoptosis in somatic cells
cancer in somatic cells (due to alterations to growth hormones and tumor suppressor genes)
defects in germ cell line that are carried by offspring

Question 3

Where are double strand breaks likely to occur?

Answer 3

at repeated sequences

Question 4

What causes double strand breaks?

Answer 4

Errors in meiosis or mitosis
Ionizing radiation
Transposable elements which leave the ends of chromosomes exposed when they are incorrectly attached.

Question 5

What are potential impacts of double strand breaks?

Answer 5

deletions or chromosomal rearrangements

Question 6

What type of chromosomal rearrangements can occur as a result of double strand breaks?

Answer 6

1. insertion
2. deletions
3. deletion and duplication of sister chromatids
4. translocation of non-homologous chromosomes

Question 7

What are the mechanisms for repairing double strand breaks?

Answer 7

1. homologous recombination
2. single strand annealing
3. alternate end joining
4. non-homologous end joining

Question 8

What happens during homologous recombination?

Answer 8

DSB are repaired via crossing over (strand invasion) using homologs as templates, resulting in perfect repairs.

Question 9

What happens during single strand annealing?

Answer 9

DSB are repaired using similar-enough single strand sequences, which can lead to deletions. This is annealing at long homologies.

Question 10

What happens during non homologous end joining?

Answer 10

Non homologous chromatids are used to cover the blunt ends. This method is accurate, but can lead to 1-4 nt deletions.

Question 11

What is alternative end joining?

Answer 11

When annealing occurs at microhomologies and blunt ends are randomly joined together. This is very problematic.