Before sequencing a biological sample, a library of the sample's DNA needs to be prepared. The library preparation procedure usually includes fragmenting the sample's DNA and labeling (tagging) of the fragments. The final library, ready for sequencing, is a collection of DNA fragments that together represent the entire genomic content of a given sample (organism or entire environment).
Library size often refers to the final → sampling depth as the number of sequenced bases after the sequencing process. Different library sizes are most likely caused by different efficiencies of the sequencing process and require → normalization.
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