One gene work as a barcode for one species and not for another because for different species different barcodes are used.
Every specie is different than another organism genetically so it also needs different barcodes for every other specie. If all the species are made up of the same gene then we can say that one barcode is used for all of them but its not the case.
Every organism has different and its own gene so one gene barcode is not acceptable for all species but for the original one so we can conclude that one barcode is used for one species and not for another.
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