Multi-Point Mapping conundrum... ACEdb defies mendels laws :-)

rd at sanger.ac.uk rd at sanger.ac.uk
Wed Nov 17 18:01:12 EST 1999

Your two questions are related.  Yes, the data in multi-pt lines such
as the one you give are only for recombinants.  If you only have a
multi-pt data object then you only get relative distance information,
not absolute distances.  If you want to score all progeny, then you
should create a separate 2-pt data object just for W and Z that gives
the numbers of recombinants and non-recombinants.  The way the 2-pt
data and multi-pt data are combined will correctly handle all the

For C. elegans, for which this system was designed, and I believe
other similar experimental systems, it is standard to only pick and
score recombinants between a pair of preselected markers when doing
multipt crosses.  At least two of the genes in the cross are picked to
have established map positions, so that the relative position
information obtained by looking only at recombinants is effectively
made absolute by having at least one fixed distance predefined.


> eg. A_not_B:   W 20 X 10 Y 5 Z
> in this example how does ACE know if the W-X interval contained 20
> recombinants out of 200, 2000, or 2 billion individuals scored??  Surely
> this is important?  or??
> Oh... and while we are on the subject, a quick clarification.  the
> numbers in the intervals - they are number of recombinants, right?  Not
> numbers of NON-recombinants...  (i.e. it is a bit confusing whether the
> number in the intervals refers to W_not_X   versus W_and_X)


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