I am wondering what do the pieces of black lines between the coverage and reads mean? Thanks if anybody knows

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Hi. They are this.

Found it on --> https://software.broadinstitute.org/software/igv/AlignmentData

> Downsampled reads areas are marked with a black rectangle just under the coverage track. The coverage track represents coverage for all the reads.

If you wanna get rid of the, go to preferences and turn off downsampling.