 Read coverage

Read coverage describes how sequencing reads overlap a target sequence. Per-base depth counts overlapping reads at each position, whereas breadth asks what fraction of target positions receives specified support. For example, high average depth can coexist with an uncovered exon if sampling is uneven. In RNA sequencing, coverage also reflects transcript abundance, processing and library preparation, so absence of reads is not automatically evidence that a genomic region is absent. ^[ref]