The LaacZ library: frequency of embryos with N events of recombination.

The validity of the LaacZ library was assessed by determining the number of embryos totally lacking SE labelling on a sample of 97 embryos. From this number (42) the number of embryos presenting N events of recombination (from 1 to 4, left column) was calculated using the fluctuation test of Luria and Delbrück (see Materials and Methods). The right column reports the observed numbers of embryos possibly corresponding to N events (see text for details).