On the Unconformity at the Base of the Ashgillian in the Bala District

The possibility of an unconformity at the base of the Ashgillian in North Wales seems to have suggested itself to several of those who have worked in that region. A definite verdict, however, has never been recorded, and the prevailing, if not general, view is that the Caradocian and Ashgillian are everywhere conformable.</jats:p

Analysis of the chromosomal distribution of transposon-carrying T-Dnas in tomato using the inverse polymerase chain-reaction

We are developing a system for isolating tomato genes by transposon mutagenesis. In maize and tobacco, the transposon Activator (Ac) transposes preferentially to genetically linked sites. To identify transposons linked to various target genes, we have determined the RFLP map locations of Ac- and Dissociation (Ds)-carrying T-DNAs in a number of transformants. T-DNA flanking sequences were isolated using the inverse polymerase chain reaction (IPCR) and located on the RFLP map of tomato. The authenticity of IPCR reaction products was tested by several criteria including nested primer amplification, DNA sequence analysis and PCR amplification of the corresponding insertion target sequences. We report the RFLP map locations of 37 transposon-carrying T-DNAs. We also report the map locations of nine transposed Ds elements. T-DNAs were identified on all chromosomes except chromosome 6. Our data revealed no apparent chromosomal preference for T-DNA integration events. Lines carrying transposons at known map locations have been established which should prove a useful resource for isolating tomato genes by transposon mutagenesis