Detailed four-way comparative mapping and gene order analysis of the canine ctvm locus reveals evolutionary chromosome rearrangements

Canine tricuspid valve malformation (CTVM) maps to canine chromosome 9 (CFA9), in a region syntenic with gene-dense human chromosome 17q. To define synteny blocks, we analyzed 148 markers on CFA9 using radiation hybrid mapping and established a four-way comparative map for human, mouse, rat, and dog. We identified a large number of rearrangements, allowing us to reconstruct the evolutionary history of individual synteny blocks and large chromosomal segments. A most parsimonious rearrangement scenario for all four species reveals that human chromosome 17q differs from CFA9 and the syntenic rodent chromosomes through two macroreversals of 9.2 and 23 Mb. Compared to a recovered ancestral gene order, CFA9 has undergone 11 reversals of <3 Mb and 2 reversals of >3 Mb. Interspecies reuse of breakpoints for micro- and macrorearrangements was observed. Gene order and content of the ctvm interval are best extrapolated from murine data, showing that multispecies genome rearrangement scenarios contribute to identifying gene content in canine mapping studies.

Gray code masks for sequencing by hybridization

In light-directed synthesis of high-density oligonucleotide arrays for sequencing by hybridization, synthesis errors result from the unintended illumination of chip regions that should remain dark. Most synthesis errors occur at the borders of illuminated regions, where light diffraction, internal reflection, and scattering produce the most unintended illumination. A combinatorial synthesis strategy based on two-dimensional Gray codes was devised to reduce the overall lengths of these borders in masks for photolithographic chip design. This article describes an application of two-dimensional Gray codes and demonstrates that masks based on this approach are optimal for minimizing the border length in VLSIPS (very large scale immobilized polymer synthesis).