How do I reference a 'selection' made within a placeholder.control.dropdownlist?

Within my aspx.cs file I create the following dropdownlist within a placeholder:

 /** create the dropdownlist for this specific time through the loop **/

DropDownList ddlSomeList = new DropDownList();

ddlSomeList.ID = "ddlSomeList";

/** add each control to the placeholder **/

placeholderexpertise.Controls.Add(ddlSomeList);

 

then during the following update statement, I want to reference what value the user has selected, I am trying the following, but, it does not work:

strUpdateQuery1 = "UPDATE ThePersonUPLOAD SET date_modified=GetDate(),expertise=@expertise WHERE person_id=@person_id";

SqlCommand UpdateReviewerC ...