Mapping a telomere using the translocation eT1(III;V) in Caenorhabditis elegans.

In Caenorhabditis elegans, individuals heterozygous for a reciprocal translocation produce reduced numbers of viable progeny. The proposed explanation is that the segregational pattern generates aneuploid progeny. In this article, we have examined the genotype of arrested embryonic classes. Using appropriate primers in PCR amplifications, we identified one class of arrested embryo, which could be readily recognized by its distinctive spot phenotype. The corresponding aneuploid genotype was expected to be lacking the left portion of chromosome V, from the eT1 breakpoint to the left (unc-60) end. The phenotype of the homozygotes lacking this DNA was a stage 2 embryonic arrest with a dark spot coinciding with the location in wild-type embryos of birefringent gut granules. Unlike induced events, this deletion results from meiotic segregation patterns, eliminating complexity associated with unknown material that may have been added to the end of a broken chromosome. We have used the arrested embryos, lacking chromosome V left sequences, to map a telomere probe. Unique sequences adjacent to the telomeric repeats in the clone cTel3 were missing in the arrested spot embryo. The result was confirmed by examining aneuploid segregants from a second translocation, hT1(I;V). Thus, we concluded that the telomere represented by clone cTel3 maps to the left end of chromosome V. In this analysis, we have shown that reciprocal translocations can be used to generate segregational aneuploids. These aneuploids are deleted for terminal sequences at the noncrossover ends of the C. elegans autosomes.     

A barcode analysis of the genus Lobophora (Dictyotales,Phaeophyceae) in the western Atlantic Ocean with four novel species and the epitypification of L. variegata (J.V. Lamouroux) E.C. Oliveira

In the western Atlantic Ocean, the brown algal genus Lobophora is currently represented by a single species, L. variegata, with a type locality designated by Lamouroux as ‘Antilles’. In this study, we used molecular-assisted alpha taxonomy (MAAT) to assess species diversity of Lobophora in Bermuda, the Florida Keys, St. Croix and Guadeloupe (Lesser Antilles). Using cox1 and cox3 sequences as barcode markers, five species of Lobophora, four of them novel, were delineated, all previously having been identified in the area as L. variegata. Our morphological and habitat studies, made possible by abundant sampling, have revealed unique characters for each of these western Atlantic species, including distinct cellular arrangements, as well as different depth ranges for certain species. Observations made from Lamouroux’s holotype of Dictyota variegata (= Lobophora variegata) allowed us to assess the anatomy of this species, which enabled us to easily align this early taxon to one of our genetic species from the western Atlantic. As the type was unavailable for genetic analysis, we selected a recent St. Croix (Virgin Is., Antilles) specimen as the epitype to support it with molecular sequence data.