dropdownlist updated based on value from another dropdownlist

I have 2 dropdown lists. I want the values in the 2nd list to change based on what's selected in the 1st.
So there would be 3 possible lists in List 2. Is there an example of how to do something like this? 

<ASP:DropDownList id="list1" runat="server">
<asp:ListItem></asp:ListItem>
<asp:ListItem >1</asp:ListItem>
<asp:ListItem >2</asp:ListItem>
<asp:ListItem >3</asp:ListItem>
</ASP:DropDownList>

<ASP:DropDownList id="list2" runat="server">
<asp:ListItem></asp:ListItem>
<asp:ListItem >1</asp:ListItem>
<asp:ListItem >2</asp:ListItem>
<asp:ListItem >3</asp:ListItem>
</ASP:DropDownList>

 
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