Note on counting crossovers:
Note that, experimentally, crossovers are only observable if they occur
in a region that will produce a distinct daughter sequence. One
crossover between a consecutive pair of variable positions will
produce the same daughter sequence as 3, 5, 7, ... crossovers.
Similarly 2, 4, 6, ... crossovers produce the same daughter sequence
as no crossovers at all. In addition, any crossovers occurring
between one end of the sequence and the first variable position are
also unable to be detected by analysis of the daughter sequence.
Typically you will find the mean number of observable
crossovers by sequence analysis of a sample of daughter sequences.
Nonetheless, the underlying true number of crossovers is also
an important statistic to know - especially when you want to try and
vary the crossover rate by making adjustments to your recombination
In DRIVeR, you can choose to enter either the mean number of
observable crossovers or the true mean number of all
crossovers. Either way, DRIVeR will also calculate and tell you the
Note also the following:
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- The maximum observable crossover rate is (M-1)/2, where
M is the number of variable positions. If the true
crossover rate is very high, then the variable positions will be
essentially randomly assigned in each daughter sequence, and all
possible daughters will be essentially equally likely (in fact you
can use GLUE instead of DRIVeR).
- Since we assume that crossovers cannot occur immediately
following a variable position (due to the nature of the reassembly
reaction), if two variable positions are adjacent in the parent
sequences, then they will remain linked in all daughter sequences
and the number of possible daughter sequences and maximum
observable crossover rate will be reduced
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