Recombination

Question 1

What is recombination?

Answer 1

homologous chromosomes bind and may or may not exchange large portions of DNA

Question 2

Only __ out of 4 chromatids can be recombinant

Answer 2

2

Question 3

Recombination occurs only between…

Answer 3

homologous regions and is highly accurate

Question 4

Recombination happens during?

Answer 4

Prophase 1 of meiosis

Question 5

What are the 3 stages of recombination?

Answer 5

Synapse, Chiasmata (holiday junctions), and resolution (recombination possible outcomes)

Question 6

synapse

Answer 6

Homologous chromosomes interact using proteins

Question 7

Chiasmata (holiday junctions)

Answer 7

point of exchange of genetic information between homologous chromosomes

Question 8

Resolution has what two possible outcomes?

Answer 8

Gene conversion and crossing-over

Question 9

Gene conversion

Answer 9

small amount of DNA exchanged corresponding to holiday junction
(mismatches can be repaired to resemble 1 allele or other homologous to match current chromosome or other

Question 10

Crossing-over

Answer 10

large amounts of DNA exchanged (everything following chiasmata site)

Question 11

Know that Holiday Junction forms what shape

Answer 11

Hexagon

Question 12

Step 1: Double-strand break formation

Answer 12

Dmc1 breaks phosphodiester bonds of both strands of one chromatid

Question 13

Dmc1

Answer 13

engages in strand exchange activity

Question 14

Step 2: resection

Answer 14

5’ ends of each broken strand are degraded to create 3’ single-stranded traits

Question 15

Step 3: first strand invasion

Answer 15

One single-strand tail invades a homologous (non-sister chromatid and forms stable heteroduplex
displacement loop (D-loop) from invaded chromatin is stabilized by single-strand binding protein

Question 16

Step 4: formation of double holiday junctions

Answer 16

D-loop enlarged by new DNA synthesis at 3’ end of invading strand
New DNA synthesis fills in gap in bottom strand using displaced strand as template

Question 17

Step 5: branch migration

Answer 17

Heteroduplex region of both DNA molecules is lengthened

Question 18

Step 6: holiday intermediate

Answer 18

we have rotation, such that holiday junction is formed

Question 19

Step 7: alternative resolutions

Answer 19

cutting of holiday junctions by endonucleases is equally likely in either vertical or horizontal plane
cutting of holiday junctions by endonucleases in either vertical or horizontal plane is equally likely

Question 20

Step 8: probability of crossover occurring

Answer 20

Non-crossover occurs when both junctions are resolved in the same plane
crossover occurs with the two junctions are resolved in different planes

Question 21

Non-crossover events occur when cuts are

Answer 21

two vertical or two horizontal

Question 22

crossover events occur when cuts are

Answer 22

one vertical, one horizontal

Question 23

Heteroduplex

Answer 23

region of DNA between breakpoints
one strand is maternal and the other is paternal
strands can have mismatches

Question 24

how to eliminate mismatches?

Answer 24

DNA repair enzymes eliminate mismatches

Question 25

Gene conversion v Crossing Over

Answer 25

Gene Conversion
Just area of heteroduplex formation exchanged
Mismatch repair can make it resemble gene original gene or other homologous gene

Crossing Over
large portions of DNA exchanged
everything after chismata site

Question 26

Purpose of recombination

Answer 26

Genetic diversity of gametes
keep homologous chromosomes together and sorted properly during meiosis 1
prevents non disjunctions during meiosis 1