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: To determine whether the capacity for reactive DNA synthesis was also subject to genetic regulation , cardiac hypertrophy was induced in the strains of mice comprising the extremes of the nuclear number survey .
### Output Text:
To determine whether the capacity for reactive DNA synthesis was also subject to genetic regulation , cardiac hypertrophy was induced in the strains of mice comprising the extremes of the nuclear number survey . 