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phastCons data files contain the compressed conservation scores that underlie the Conservation annotation track and the phastCons table. For a detailed description of the algorithm used to produce the scores, see the Genome Browser description page associated with the Conservation track.
File Format (assemblies released Nov. 2004 and later)
When uncompressed, the file contains a declaration line and one column of data in wiggle table fixed-step format:
fixedStep chrom=scaffold_1 start=3462 step=1 0.0978 0.1588 0.1919 0.1948 0.1684
The declaration line specifies the starting point of the data in the assembly. It consists of the following fields:
A new declaration line is inserted in the file when the chrom value changes, when a gap is encountered (requiring a new start value), or when the step interval changes.
Data lines The first data value below the header shows the score corresponding to the position specified in the header. Subsequent score values step along the assembly in one-base intervals. The score shows the posterior probability that the phylogenetic hidden Markov model (HMM) of phastCons is in its most-conserved state at that base position.
When uncompressed, the data file contains two columns:
294 0.0953 295 0.0948 296 0.0943 297 0.0936 298 0.0929 299 0.0921
Column #1 contains a one-based position coordinate. Column #2 contains a score showing the posterior probability that the phylogenetic hidden Markov model (HMM) of phastCons is in its most conserved state at that base position.
References for phastCons
Siepel A and Haussler D (2005). Phylogenetic hidden Markov models. In R. Nielsen, ed., Statistical Methods in Molecular Evolution, pp. 325-351, Springer, New York.
Siepel, A., Bejerano, G., Pedersen, J.S., Hinrichs, A., Hou, M., Rosenbloom, K., Clawson, H., Spieth, J., Hillier, L.W., Richards, S., Weinstock, G.M., Wilson, R. K., Gibbs, R.A., Kent, W.J., Miller, W., and Haussler, D. Evolutionarily conserved elements in vertebrate, insect, worm, and yeast genomes. Genome Res. 15, 1034-1050 (2005).
For a discussion of the methods used to calculate the phastCons scores, see the description page for the hg17 Conservation track in the Genome Browser.