recombination

Question 1

when does homologous recombination occur

Answer 1

prophase of meiosis 1- DNA already replicated

Question 2

crossing over is visible at

Answer 2

chiasmata

Question 3

if non homologous recombination occurs..

Answer 3

sterile

Question 4

what is involved in homologous combination

Answer 4

the breaking and joining of DNA -reciprocal and causes genetic rearrangement

Question 5

for recombination to occur..

Answer 5

homologous sequences must be present

Question 6

homologous combination is an important part of..

Answer 6

-meiosis and variation -DNA repair

Question 7

to repair non-homologous end joining

Answer 7

the double strand is broken. degradation after this causes a loss of nucleotides, but because the two lengths are now straight instead of ‘sticky’, the double strand can rejoined by ligase enzymes–> there will be some deletion of DNA sequence

Question 8

homologous recombination can..

Answer 8

repair double strands

Question 9

homologous recombination-simple

Answer 9

sister chromatid is positioned next to the double stranded break. There is a loss of nucleotides due to degradation, which removes the ‘sticky’ ends. When the ends have been processed, homologous recombination occurs and the damage is repaired accurately using inform from sister chromatid

Question 10

linkage analysis

Answer 10

genes on a chromosome are linked (physically and genetically). For two linked genes: recombination is proportional to distant apart. Therefore if we measure RF, we can map genes

Question 11

for two linked genes:

Answer 11

recombination is proportional to distant apart. Therefore if we measure RF, we can map genes

Question 12

RF

Answer 12

recombination frequency

Question 13

Gene targetting

Answer 13

we can target specific genes for mutations in vivo. DNA is introduced which contains: homologous sequences and selectable markers. The DNA is then integrated into the DNA causing recombination

Question 14

In circular DNA

Answer 14

only single crossovers

Question 15

in linear DNA

Answer 15

double crossover- and a gene will be deleted

Question 16

detailed: how does meiotic homologous recombination generate crossovers

Answer 16

1) paired chromosomes are adjacent to each other 2)enzymes cause one of the double strands to break 3) exonuclease expose single stranded 3’ end 4) another enzyme causes the strand to invite the other double strand on the other chromosome 5) this produces a d loop 6)DNA synthesis occurs - forming a holiday junction 7) DNA ligase cuts either across the junction or diagonally down

Question 17

holliday junction

Answer 17

a cross-shaped structure tat forms during genetic recombination- when two double stranded DNA molecules (chromosomes) becomes separated into four strands in order to exchange segments of genetic information

Question 18

depending on the way the holiday junction is cut there will either be

Answer 18

cross over or no crossover

Question 19

if both chromosomes are cut horizontally

Answer 19

no crossover

Question 20

if the chromosomes are cut diagonally

Answer 20

crossover

Question 21

double strand break repair by homologous recombination (part 1)

Answer 21

• first one of the chromatid double strand breaks
• exonucleases degraded 5’ en
• the overly 3’ end that ahsnt been degrades, invades the sister chromatid strand
• when they cross it is called a branch point and this heteroduplex is called a D- loop is formed
  
  • then dna sytnehsis and migration of the branch point occurs

Question 22

double strand break repair by homologous recombination

(part 2)

Answer 22

• continued branch migration, followed by pairing off newky synthesised DNA with tip strand synthesis
  
  • DNA; ligation - DNA Ligase attaches new DNA

Question 23

Heteroduplex formation in homologous recomibination

Answer 23

1. synapsis is catalysed by RAD51 and other proteins
2. binds to single stranded 3’ end of damaged DNA
3. forms a dynamic 3-stranded structutre with double stranded DNA
4. searches for homology
5. Heteroduplex formation

Question 24

heteroduplex

Answer 24

a double stranded moelcule of nucleic acid originated through the egentic recombination of single complememntary strands (form homologous chromsosomes) derived from different sources

Question 25

in circular DNA there will be a

Answer 25

single crossover

Question 26

in linear DNA there will be

Answer 26

a double crossover

Question 27

for two linked genes combination is proportional to

Answer 27

distance apart- therefre we measure recombination frequency

-therefore we can map genes

Question 28

holiday junction formed in

Answer 28

the repairof a souble strand break

Question 29

heteroduplex synapsis is catalysed by

Answer 29

Rad51 and othe rproteins