input type checkbox vs asp:checkbox

Can someone explain this reaction. I try to dynamically put an asp:checkbox in the CS file. I don't see it on the page. compared to the input type checkbox that works fine.

What is my issue?

Here are the 2 lines:

Response.Write("    <div class='userList'><input type='checkbox' id='chk' value='" + row["id"].ToString() + "' "+ isChecked +" /></div>");
Response.Write("    <div class='userList'><asp:CheckBox ID='Cb' runat='server' /></div>");

Thanks for the help