Two new genetic balancers for chromosome II of Caenorhabditis elegans were isolated and characterized. mIn1 was shown to be an inversion of a large central portion of the chromosome, extending from lin-31
, that includes most of the genes on the chromosome. It balances a region to the left of the gene cluster that was previously not covered by any of the available balancers. mIn1 recombines efficiently with the normal chromosome II in regions outside the rearrangement at both ends, and appears to enhance recombination frequency adjacent to the inversion breakpoints. Eight variant strains of mIn1 were isolated, including forms that carry recessive morphological or lethal markers, an unmarked form, and one that carries an integrated transgene that confers a semi-dominant green fluorescent protein (GFP) phenotype. This set of variants makes mIn1 useful for a wide variety of applications. The second balancer, mT1, was shown to be a II; III translocation that suppresses recombination on the right arms of chromosomes II and III. It balances chromosome II from the region between bli-2
to the right end of the chromosome, and chromosome III from the region between daf-2
to the right end. These rearrangements provide the means to stabilize efficiently most of the genes on chromosome Il and may be useful for studies of chromosome pairing and recombination.