Availability of the human genome sequence and high similarity between humans and pigs at
the molecular level provides an opportunity to use a comparative mapping approach to
piggy-BAC the human genome. In order to advance the pig genome sequencing initiative,
sequence similarity between large-scale porcine BAC-end sequences (BESs) and human
genome sequence was used to construct a comparatively-anchored porcine physical map that
is a first step towards sequencing the pig genome. A total of 50,300 porcine BAC clones
were end-sequenced, yielding 76,906 BESs after trimming with an average read length of
538 bp. To anchor the porcine BACs on the human genome, these BESs were subjected
to BLAST analysis using the human draft sequence, revealing 31.5% significant hits
between the human and porcine genomes. Porcine BESs with unique homology matches
within the human genome provided a source of markers spaced approximately 70 to
300 kb along each human chromosome. In order to evaluate the utility of piggy-BACing
human genome sequences, and confirm predictions of orthology, 193 evenly spaced BESs
with similarity to HSA3 and HSA21 were selected and then utilized for developing a
high-resolution (1.22Mb) comparative radiation hybrid map of SSC13 that represents a
fusion of HSA3 and HSA21. Resulting RH mapping of SSC13 covers 99% and 97% of
HSA3 and HSA21, respectively. Seven evolutionary conserved blocks were identified
including six on HSA3 and a single syntenic block corresponding to HSA21. The strategy
of piggy-BACing the human genome described in this study demonstrates that through
a directed, targeted comparative genomics approach construction of a high-resolution
anchored physical map of the pig genome can be achieved. This map supports the selection
Using the INRA–Minnesota porcine radiation hybrid panel, we have constructed a human–pig comparative map composed of 2274 loci, including 206 ESTs and 2068 BAC-end sequences, assigned to 34 linkage groups. The average spacing between comparative anchor loci is 1.15 Mb based on human genome sequence coordinates. A total of 51 conserved synteny groups that include 173 conserved segments were identified. This radiation hybrid map has the highest resolution of any porcine map to date and its integration with the porcine linkage map (reported here) will greatly facilitate the positional cloning of genes influencing complex traits of both agricultural and biomedical interest. Additionally, this map will provide a framework for anchoring contigs generated through BAC fingerprinting efforts and assist in the selection of a BAC minimal tiling path and assembly of the first sequence-ready map of the porcine genome.