= 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. <Talking Glossary of Genomic and Genetic Terms by NHGRI>[Coverage entry]{ref}
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