Chimeras can be considered artifacts and be filtered out from the data during processing [1] to prevent spurious inferences of biological variation.
It is usually considered to be a contaminant in transcript and expressed sequence tag (which results in the moniker of EST chimera) databases.
[5] It is estimated that approximately 1% of all transcripts in the National Center for Biotechnology Information's Unigene database contain a "chimeric sequence".
[7] PCR chimeras are an important issue to take into account during metabarcoding, where DNA sequences from environmental samples are used to determine biodiversity.
In this case, the most common mechanism of chimera formation is that incomplete extension during the PCR results in partial sequence strands that can act as primers in subsequent PCR cycles on similar but non identical sequences.