[monolithed]

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.5.2/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(function() {
   $("select[name='select']").change(function() {
       $("input[name='checkbox1']").attr('checked', this.value == 1 ? 'checked' : '');
    });
});
</script>

<form name="" action="" method="">
    <select name="select">
        <option value="0">0</option>
        <option value="1">1</option>
        <option value="2">2</option>
    </select>
    
    <input type="checkbox" name="checkbox1" />
    <input type="checkbox" name="checkbox2" />
    <input type="checkbox" name="checkbox1" />
</form>