LG II balancer chromosomes in Caenorhabditis elegans: mT1(II;III) and the mln1 set of dominantly and recessively marked inversions

Two new genetic balancers for chromosome II of Caenorhabditis elegans were isolated and characterized. mIn1 was shown to be an inversion of a large ce ntral portion of the chromosome, extending from lin-31 to rol-1, that inclu des most of the genes on the chromosome. It balances a region to the left o f the gene cluster that was previously not covered by any of the available balancers. mIn1 recombines efficiently with the normal chromosome II in reg ions outside the rearrangement at both ends, and appears to enhance recombi nation frequency adjacent to the inversion breakpoints. Eight variant strai ns of mIn1 were isolated, including forms that carry recessive morphologica l or lethal markers, an unmarked form, and one that carries an integrated t ransgene that confers a semi-dominant green fluorescent protein (GFP) pheno type. This set of variants makes mIn1 useful for a wide variety of applicat ions. The second balancer, mT1, was shown to be a II; III translocation tha t suppresses recombination on the right arms of chromosomes II and III. It balances chromosome II from the region between bli-2 and dpy-10 to the righ t end of the chromosome, and chromosome III from the region between daf-2 a nd unc-93 to the right end. These rearrangements provide the means to stabi lize efficiently most of the genes on chromosome Il and may be useful for s tudies of chromosome pairing and recombination.