The four single-nucleotide mutations tracks have a default viewing range of score 10 to 50. As explained in the paragraph above, that results in slightly less than 10% of the data displayed which helps visualization. The deletion and insertion tracks have a default filter of 10-100 since they display discrete items and not graphical data.
Single nucleotide variants (SNV): For SNVs, at every
genome position, there are three values per position, one for every possible
nucleotide mutation. The fourth value, "no mutation", representing
the reference allele, e.g. A to A, is always set to zero.
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When using this track, zoom in until you can see every basepair at the top of the display. Otherwise, there are several nucleotides per pixel under your mouse cursor and instead of an actual score, the tooltip text will show the average score of all nucleotides under the cursor. This is indicated by the prefix "~" in the mouseover. Averages of scores are not useful for any application of CADD.
Insertions and deletions: Scores are also shown on mouseover for a set of insertions and deletions. On hg38, the set has been obtained from Gnomad3. On hg19, the set of indels has been obtained from various sources (gnomAD2, ExAC, 1000 Genomes, ESP). If your insertion or deleletion of interest is not in the track, you will need to use CADD's online scoring tool to obtain them.