1. A SINGLE homologous recombination event
MOLECULAR LEVEL:
A SINGLE homologous recombination event
EACH CROSSOVER RESOLVED SEPARATELY
AT HOLLIDAY JUNCTIONS
Heteroduplex
DNA
Equivalent view
Rotate bottom 180 degrees
to the left, will = this.
Pretend grab lower right blue with hand,
pull toward you at middle,
put down again on left side

2. Cont’d: MOLECULAR LEVEL: A SINGLE homologous recombination event
Once you have rotated the Holliday junction,
Last step is to cleave 2 of the strands.
The site where you cleave determines the outcome.
If you
cut here
(THICK strands)
If you
cut here
(thin strands)
THICK strands
of homologs
re-ligate
Thin strands
of homologs
re-ligate
THICK strand
becomes
recombinant
Thin strand
becomes
recombinant
Note: this does not necessarily = a recombinant CHROMOSOME!

3. One possible outcome from resolution of
Holliday Junctions
Heteroduplex
DNA
IF YOU CLEAVE HERE: (at THICK strands only)
RESULT: Chr w/ heteroduplex DNA, but NO overall recomb event
Need to recomb both single strands to = chr recombination. a b a’ b’ A’ B’ A B

4. Another possible outcome from resolution of
Holliday Junctions
Heteroduplex
DNA
IF YOU CLEAVE HERE: (at thin strands only)
RESULT: Chr w/ heteroduplex DNA, but NO overall recomb event
Need to recomb both single strands to = chr recombination. a b a’ b’ A’ B’ A B

5. Another possible outcome from resolution of
Holliday Junctions
Heteroduplex
DNA
IF YOU CLEAVE HERE: (one site cleaves THICK, one site cleaves thin)
RESULT: Chr w/ heteroduplex DNA + SINGLE recombination event.
Both single strands recombined to = chr recombination. a B a’ B’ A’ b’ A b