In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Therefore , we conducted an analysis of the association of the 5 - HT6 gene ( HTR6 ) with METH - induced psychosis .
### Output Text:
Therefore , we conducted an analysis of the association of the <span class="chemical">5 - HT6</span> gene ( HTR6 ) with <span class="chemical">METH</span> - induced psychosis . 