I'm looking at phyloP data from UCSC (http://hgdownload.cse.ucsc.edu/goldenPath/mm9/phyloP30way/vertebrate/). It looks like the first 3 million bases or so of some chromosomes don't have phyloP scores. Example:
$ zcat chr1.phyloP30way.wigFix.gz | head -n 5
fixedStep chrom=chr1 start=3000306 step=1
so the start position is 3000306. Why are there no scores for position 1 through 3000305?