Historical droughts recorded in extended Juniperus procera ring-width chronologies from the Ethiopian Highlands.

In the Horn of Africa, little is known about temporal changes in hydroclimate owing to the influence of multiple weather systems, the complex terrain, and the sparse instrumental records. Absolutely dated tree-ring records offer the potential to extend our understanding of climate into the pre-instrumental era, but tree-ring studies in this region, and indeed all of tropical Africa, have been rare largely due to lack of an annual climate cycle that reliably produces annual tree-rings. In this study, 40 cores were obtained from 31 Juniperus procera trees growing in the grounds of Ethiopian Orthodox Tewahedo churches in the Gonder region of Ethiopia. The samples were cross-dated using a re-iterative process involving identifying anatomical features from high-resolution images. The tentative ring-width chronologies were revised after the determination of bomb-peak accelerator mass spectrometry radiocarbon dates. Individual series were significantly correlated to the respective master chronologies (r > 0.55; P < 0.05), and expressed population signal values ranged from 0.55 to 0.92. Historical drought years were successfully traced in the chronologies by pointer year analysis. This study confirms that Juniperus procera growing in areas of unimodal precipitation exhibits annual tree-rings and offers the potential as an indirect measure of past climate.

Mouse BAC ends quality assessment and sequence analyses.

A large-scale BAC end-sequencing project at The Institute for Genomic Research (TIGR) has generated one of the most extensive sets of sequence markers for the mouse genome to date. With a sequencing success rate of >80%, an average read length of 485 bp, and ABI3700 capillary sequencers, we have generated 449,234 nonredundant mouse BAC end sequences (mBESs) with 218 Mb total from 257,318 clones from libraries RPCI-23 and RPCI-24, representing 15x clone coverage, 7% sequence coverage, and a marker every 7 kb across the genome. A total of 191,916 BACs have sequences from both ends providing 12x genome coverage. The average Q20 length is 406 bp and 84% of the bases have phred quality scores > or = 20. RPCI-24 mBESs have more Q20 bases and longer reads on average than RPCI-23 sequences. ABI3700 sequencers and the sample tracking system ensure that > 95% of mBESs are associated with the right clone identifiers. We have found that a significant fraction of mBESs contains L1 repeats and approximately 48% of the clones have both ends with > or = 100 bp contiguous unique Q20 bases. About 3% mBESs match ESTs and > 70% of matches were conserved between the mouse and the human or the rat. Approximately 0.1% mBESs contain STSs. About 0.2% mBESs match human finished sequences and > 70% of these sequences have EST hits. The analyses indicate that our high-quality mouse BAC end sequences will be a valuable resource to the community.