Worm Breeder's Gazette 9(2): 27

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Physical Map of the Genome

A. Coulson, John Sulston, et al.

Figure 1

The map has advanced relatively slowly in the last six months, 
because we have been experimenting with means to preselect clones for 
fingerprinting.  Our preferred technique is to prepare six master 
nitrocellulose filters (150 mm), carrying about 5,000-10,000 clones 
each and replicate them onto four sets of nylon filters.  The masters 
are glycerinated and frozen; the copies are processed for 
hybridization.  Probes are made by mixing fragments from (usually ten) 
unattached clones or clones at the ends of contigs.  One set of films 
is deliberately overexposed, without a screen, so as to make a sharp 
image of all the colonies to serve as a template.  Films from 
subsequent probings are exposed only enough to show a faint background;
they are then aligned with the template films and the positive clones 
are marked on the latter.  With the marked template positioned above 
its master filter and a suitably positioned lamp, one can align the 
pattern, sight through the mark to the corresponding master colony and 
pick correctly more or less every time.  This method avoids the need 
to rescreen (if any clone is picked erroneously it will simply fail to 
overlap with the probe in subsequent fingerprinting) and so allows a 
satisfactory throughput.  However, we feel that random cloning is 
still slightly more effective at present and are going back to that 
for the moment.  We are processing clones faster now, as a result of 
getting a computerized film scanner working and of preparing cosmid 
DNA in microtitre wells.

Figure 1