Description

This track shows alignments of the human genome with itself, using a gap scoring system that allows longer gaps than traditional affine gap scoring systems. The system can also tolerate gaps in both sets of sequence simultaneously. After filtering out the "trivial" alignments produced when identical locations of the genome map to one another (e.g. chrN mapping to chrN), the remaining alignments point out areas of duplication within the human genome. The pseudoautosomal regions of chrX and chrY are an exception: in this assembly, these regions have been copied from chrX into chrY, resulting in a large amount of self chains aligning in these positions on both chromosomes.

The chain track displays boxes joined together by either single or double lines. The boxes represent aligning regions. Single lines indicate gaps that are largely due to a deletion in the query assembly or an insertion in the target assembly. Double lines represent more complex gaps that involve substantial sequence in both the query and target assemblies. This may result from inversions, overlapping deletions, an abundance of local mutation, or an unsequenced gap in one of the assemblies. In cases where multiple chains align over a particular region of the human genome, the chains with single-lined gaps are often due to processed pseudogenes, while chains with double-lined gaps are more often due to paralogs and unprocessed pseudogenes.

In the "pack" and "full" display modes, the individual feature names indicate the chromosome, strand, and location (in thousands) of the match for each matching alignment.

Display Conventions and Configuration

By default, the chains to chromosome-based assemblies are colored based on which chromosome they map to in the aligning organism. To turn off the coloring, check the "off" button next to: Color track based on chromosome.

To display only the chains of one chromosome in the aligning organism, enter the name of that chromosome (e.g. chr4) in box next to: Filter by chromosome.

Methods

The genome was aligned to itself using blastz. Trivial alignments were filtered out, and the remaining alignments were converted into axt format using the lavToAxt program. The axt alignments were fed into axtChain, which organizes all alignments between a single target chromosome and a single query chromosome into a group and creates a kd-tree out of the gapless subsections (blocks) of the alignments. A dynamic program was then run over the kd-trees to find the maximally scoring chains of these blocks. The following matrix was used:

	A	C	G	T
A	91	-114	-31	-123
C	-114	100	-125	-31
G	-31	-125	100	-114
T	-123	-31	-114	91

Credits

Blastz was developed at Pennsylvania State University by Minmei Hou, Scott Schwartz, Zheng Zhang, and Webb Miller with advice from Ross Hardison.

Lineage-specific repeats were identified by Arian Smit and his RepeatMasker program.

The axtChain program was developed at the University of California at Santa Cruz by Jim Kent with advice from Webb Miller and David Haussler.

The browser display and database storage of the chains were generated by Robert Baertsch and Jim Kent.

References

Chiaromonte, F., Yap, V.B., Miller, W. Scoring pairwise genomic sequence alignments. Pac Symp Biocomput 2002, 115-26 (2002).

Kent, W.J., Baertsch, R., Hinrichs, A., Miller, W., and Haussler, D. Evolution's cauldron: Duplication, deletion, and rearrangement in the mouse and human genomes. Proc Natl Acad Sci USA 100(20), 11484-11489 (2003).

Schwartz, S., Kent, W.J., Smit, A., Zhang, Z., Baertsch, R., Hardison, R., Haussler, D., and Miller, W. Human-Mouse Alignments with BLASTZ. Genome Res. 13(1), 103-7 (2003).