English to French Medical Medical (general)

Je ne vois pas le sens de ce terme !
Voici le contexte :

RDA involves making DNA representations from diseased and normal tissue. Then the DNA from the diseased tissue is ligated to a primer sequence and hybridized with an excess of unligated representations from the normal tissue DNA. Unique sequences are preferentially amplified during subsequent rounds of PCR and a difference product is produced which can be detected for example on an agarose gel.

Merci beaucoup.