Lecture 5: DNA Replication, Repair and Recombination 3

Question 1

_____ and _____ can occur in the same chromosome

Answer 1

crossing over; gene conversion

Question 2

What does meiotic recombination occur with?

Answer 2

Paired maternal and paternal homologous chromosomes

Question 3

What does homologous recombination mean?

Answer 3

to generate DNA molecules of novel sequence

Question 4

What is the holiday junction?

Answer 4

DNA intermediate containing four DNA strands form two different helices

Question 5

What are the two outcomes of resolution in homologous recombination?

Answer 5

• crossing over (rare)

- gene conversion (90% of Holliday junctions resolve this way)

Question 6

What happens if both strands in each Holliday junction are cut in the same way?

Answer 6

They will separate with minimal exchange of sequences

Question 7

What happens if strands in the Holliday junction are cut in opposite directions?

Answer 7

portions of each chromosome upstream and downstream are swapped, yielding crossing over

Question 8

Once strand invasion occurs, the points of exchange can _______

Answer 8

move through branch migration

Question 9

What happens in branch migration?

Answer 9

unpaired regions of one single strand displaces a paired region on the other

Question 10

What is heteroduplex DNA?

Answer 10

region where a strand from the maternal homolog is base paired with a strong from the paternal homolog

Question 11

What is gene conversion?

Answer 11

divergence from the expected distribution of alleles during meiosis

Question 12

How does gene conversion occur?

Answer 12

• DNA synthesis during homologous recombination

- Repair of mismatches in regions of heteroduplex DNA

Question 13

What are the three types of transpositional recombination?

Answer 13

• DNA only transposons
• Retroviral like retrotransposons
• nonretroviral like retrotransposons

Question 14

Structure, enzyme and mode of movement for DNA only transposons

Answer 14

Structure: short inverted repeats at each end

enzyme: transposes
movement: moves as DNA, either by cut and paste or replicative pathways

Question 15

Structure, enzyme and mode of movement for nonretroviral like retrotransposons

Answer 15

structure: poly A at 3’ end of RNA transcript, 5’ end is ofter truncated
enzyme: reverse transcriptase and endonuclease
moves: via an RNA intermediate that is often synthesized from a neighboring promoter

Question 16

Structure, enzyme and mode of movement for retroviral like retrotransposons

Answer 16

structure: directly repeated long terminal repeats at each end
enzyme: reverse transcriptase and integrase
moves: via an RNA intermediate who’s production is driven by a promoter in the LTR

Question 17

When two transposase molecules come together forming a loop juxtaposing two ends of element it forms a _____

Answer 17

transpososome

Question 18

What does conservative site specific recombination do?

Answer 18

mediates rearrangements of other types of mobile DNA elements

Question 19

How does conservative site specific recombination differ from transposition?

Answer 19

• need special sites on each DNA that serve as recognition sites for recombinase
• form transient high energy covalent bonds and use this energy to complete DNA arrangement

Question 20

What does the outcome of conservative site specific recombination depend on?

Answer 20

orientation of the insertion site

Question 21

If site are in the same orientation, then DNA sequence can ______

Answer 21

be integrated or excised

Question 22

If sites are inverted in orientation, then DNA sequence is ______

Answer 22

inverted instead of excised