SO fiddle

Test Fiddle mainly for SO Questions

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/overcast/jquery-ui.css">
<form action="/form/update" name="update-form" method="POST"> 

<select name="menu1_selection"> 
<option value="">-</option> 
<option value="1">1</option> 
<option value="2">2</option> 
<option value="3">3</option> 
<option value="4">4</option> 
<option value="5">5</option> 
<option value="6">6</option> 
<option value="7">7</option> 
<option value="8">8</option> 
<option value="9">9</option> 
<option value="10">10</option> 
<option value="11">11</option> 
<option value="12">12</option> 
</select>

<select name="menu2_selection"> 
<option value="">-</option> 
<option value="1">1</option> 
<option value="2">2</option> 
<option value="3">3</option> 
<option value="4">4</option> 
<option value="5">5</option> 
<option value="6">6</option> 
<option value="7">7</option> 
<option value="8">8</option> 
<option value="9">9</option> 
<option value="10">10</option> 
<option value="11">11</option> 
<option value="12">12</option> 
</select>

<a href="#" onclick="return false;" class="copyMenu1">copy</a>

</form>

JavaScript

$(function() {  
  $("a.copyMenu1").click(function(){
    $("select[name='menu1_selection']").val($("select[name='menu2_selection']").val());
  });
});