Add checkboxlist item onclick of another checkbox - asp.net

Question

I'm just wondering if there's a way to add a new checkbox item to an existing asp:checkboxlist control, when another checkbox is checked, without having to do a full postback of the page. Whether it's with javascript, jquery, ajax. Just wondering how (if at all) I can do something like this.
I've been doing some research and it appears I can do a partial postback using an asp:UpdatePanel. I've never used one of these before. Does anyone have an example of how they can be used? Here's what I have, but it's still doing a full postback
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<tr>
<td width="50%">
<asp:CheckBox runat="server" ID="chkEnglish" Font-Bold="true" TextAlign="Right" Text=" English" />
</td>
<asp:Panel runat="server" ID="pnlTopLanguages">
<td rowspan="3" valign="top">
<asp:CheckBoxList ID="chkTopLanguages" CssClass="cb chkTopLangs" TextAlign="Right" runat="server" />
<asp:TextBox runat="server" ID="txtOtherLanguages" onkeyup="SetButtonStatus(this)" onclick="return clearLanguageSearchText()" Text="Other Languages..."></asp:TextBox>
<asp:Button runat="server" ID="btnAddLang" Text="Add" OnClientClick="return CopyOtherLangs()" Enabled="false" /><br /><br />
<asp:CheckBox runat="server" ID="chkManyOtherLanguages" CssClass="cb" Font-Bold="true" Text="Many other languages" />
<cc3:AutoCompleteExtender ID="aceSearch" runat="server" MinimumPrefixLength="1" TargetControlID="txtOtherLanguages"
ServicePath="~/controls/wsCommunity.asmx" ServiceMethod="GetLanguageCompletionList"></cc3:AutoCompleteExtender>
</td>
</asp:Panel>
</tr>
</ContentTemplate>
</asp:UpdatePanel>

Answer 1

Building off Adils answer...to add a checkbox on check of another one, you can use:
$(".classOfCheckboxList").change(function() {
$(this).append("<input type='checkbox' id='newbox' class='currentclass' value='someval' />");
});
As Adil said, this new dynamically added box wont be accessible in the code-behind.