chapter 13 exam 2 : recombination

Question 1

What is homologous recombination?

Answer 1

Exchange of DNA through crossing over of homologous chromosomes

Question 2

What is the function of homologous recombination?

Answer 2

1. Also used for repair, especially double-stranded breaks (DSBs)
2. Maintaining diversity in sexually reproducing organisms (meiosis)
3. Mate-type switching
4. Diversity in avoidance and detection mechanisms
5. Adaptation of genes to avoid host immune system
   * •Novel invasion proteins
6. Adaptation of genes to detect pathogens
   * •Novel recognition proteins
   * Antibodies detect antigens. If bacteria change antigens, host needs new antibodies.

Question 3

Lesions in the template strand lead to 4 outcomes.

Answer 3

1. Continue through the lesions –> perpetuate mutation
2. Repair is initiated (partial repair) –> DSB
3. Fork stalling –> wait for repair
4. Lesion bypass –> single stranded gap

Question 4

Homologous repair mechanism:

Answer 4

1.Create 3’ overhangs
2.3’ end strand invasion via recombinase
•Formation of D loop
3.3’ end strand invasion of other strand invasion
•Formation of D loop
4.Strand extension via polymerase

Question 5

What are the 2 repair pathways of homologous repairs?

Answer 5

1.Synthesis-dependent strand annealing (SDSA)
•Homologs separate
•Finish polymerase and ligase
2. “Classic” DSBR pathway
•Homologs stay together and resolve holiday junctions
1.No crossover
2.Crossover

Question 6

Holiday junctions are broken via ______

Answer 6

resolvase

Question 7

How is recombination used in meiosis?

Answer 7

Recombination is also used to maintain diversity in sexually reproducing organisms

Question 8

What is crossing over and when does it happen?

Answer 8

• Crossing over happens in prophase I of meiosis I
• Between homologous chromosomes or homologs
• 2 homologs have the same genes, but potentially different alleles

Question 9

2 homologs may have the same _____ but potentially different ______

Answer 9

genes ; alleles

Question 10

When does crossing over occur?

Answer 10

Prophase I of meiosis I

Question 11

What does crossing over occur between?

Answer 11

Homologous chromosomes or homologs

Question 12

Regions of cross over are spaced apart to avoid ________

Answer 12

interference

Question 13

Does crossing over occur between homologs or sister chromatids?

Answer 13

homologs, (not sister chromatids)

Question 14

On average, how many crossovers occur per arm?

Answer 14

1

Question 15

Does cross over have to occur at least once per arm?

Answer 15

yes

Question 16

In meiosis I ______ ______ separate

Answer 16

homologous chromosomes

Question 17

What separates in meiosis II?

Answer 17

sister chromatids

Question 18

What is the result of meiosis?

Answer 18

4 unidentical, haploid cells

Question 19

What does haploid mean?

Answer 19

having only one copy of genetic material

Question 20

How is haploid represented?

Answer 20

n

Question 21

How is diploid represented

Answer 21

2n

Question 22

what does diploid mean?

Answer 22

having 2 copies of genetic material

Question 23

Meiotic recombination occurs during what pathway?

Answer 23

classic DSBR pathway

Question 24

Does meiotic recombination occur during the SDSA pathway?

Answer 24

No, it occurs during the classic DSBR pathway

Question 25

What are the steps of meiotic recombination?

Answer 25

1.In early prophase I, double stranded breaks are introduced •Certain “hotspots” are more commonly broken •Thus, non-random, but not always predictable 2.3’ overhangs created 3.Strand invasion 4.Extension via polymerase 5.Double cross over intermediate (2 holiday junctions) 6.Resolution 1.Non-crossover (same as SDSA) 2.Crossover

Question 26

What is gene conversion?

Answer 26

Nonreciprocal transfer of genetic information

Question 27

What does crossing over maintain?

Answer 27

Genetic diversity!

Question 28

What is mitotic crossover?

Answer 28

* Damage during mitosis can lead to crossover events—for the sake of repair * SDSA is most common

Question 29

Is SDSA common in meiosis or mitosis?

Answer 29

mitotic division

Question 30

Describe DSBR and mating type switching

Answer 30

•Yeast (S. cervisiae )exists as 2 possible mate types: 1.Matα 2.Mata •Yeast can convert between either type through DSBR •Each mate type is stored as a pseudogene •HMLα •HMRa

Question 31

What is used when untimely breaks occur?

Answer 31

NHEJ (non homologous end joining)

Question 32

When is NHEJ used?

Answer 32

When DSBs occur when homologous chromosomes aren't available for recombination

Question 33

Describe NHEJ:

Answer 33

* Common in eukaryotes * Few prokaryotes * Common in G0 and G1 * Times when homologous chromosomes aren’t paired * Mutagenic process = DNA is not the same as it was * Loss of function of NHEJ genes promotes cancer

Question 34

Loss of function of NHEJ genes ______ cancer

Answer 34

promotes

Question 35

What does a mutagenic process mean?

Answer 35

The DNA is not the same as it was

Question 36

When is NHEJ common?

Answer 36

eukaryotes, and G0 and G1 (when homologous chromosomes aren't paired) - not as common in prokaryotes

Question 37

What are the steps of NHEJ?

Answer 37

1. Recognition of damage via Ku proteins 2. Cleaning of ends via Artemis •Creation of blunt ends 3. Creation of 3’ over hang 4. Polymerase 5. End joining via ligase

Question 38

What joins the ends in NHEJ?

Answer 38

ligase

Question 39

What cleans the ends in NHEJ?

Answer 39

Artemis

Question 40

What recognizes damage in NHEJ?

Answer 40

Ku proteins

Question 41

What does artemis cleaning the ends in NHEJ lead to?

Answer 41

Blunt ends

Question 42

B cells and T cells are immune cells that must recognize an infinite diversity of ______ ______

Answer 42

invading proteins

Question 43

Intentional NHEJ called V(D)J recombination creates random novel versions of ______ _____

Answer 43

Recognition proteins | - body randomly mixes recognition genes so they are not surprising by novel invading proteins

Question 44

What is another term for recognition protein?

Answer 44

antibody

Question 45

How is genome editing used in targeting DSBs?

Answer 45

- used to target DSBs to activate or inactivate or modify genes. - used in CRSPR, zinc fingers, and TALENS