Time of Recombination in the DROSOPHILA MELANOGASTER Oocyte. III. Selection and Characterization of...

The procedure for the selection of a temperature-sensitive recombination mutant in Drosophila is described. Use of this procedure has led to the recovery of three alleles at a new recombination locus called rec-1, located within the region of chromosome 3 circumscribed by Deficiency (3R)sbd(105). One allele, rec-1(26), is temperature sensitive, and the other two alleles, rec-1(6) and rec-1(16), are temperature insensitive. Gene dosage studies reveal rec-1(26) to be a leaky mutant with greater recombination activity in two doses than in one. The other two alleles show no dose response, implying that they may be null mutants. The temperature response curves of rec-1(26) as a homozygote and in heteroallelic combination with rec-1(16) suggest that the sharp decrease in recombination between 28 degrees and 31 degrees indicates temperature denaturation of an enzyme or other protein specified by the mutant and associated with the recombination process. The ability of small changes in temperature to reverse or abolish polarity in recombination along the X chromosome arm in rec-1( 26)/rec-1(16) females brings into question the use of the "polarity" criterion to partition mutants into two functional types, i.e., precondition mutants that display polarity and exchange mutants that do not. Evidence that rec-1 may be part of a complex locus residing in a chromosome segment harboring a variety of recombination-related genes is presented.