terveg,
<!DOCTYPE HTML>
<html>
<head>
<title>blank</title>
<meta charset="utf-8">
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<script>
$(function () {
$("#form1").on("click", "input:checkbox",function (event) {
var $indx = $("input:checkbox").index(this);
$indx++;
$("#select1 option:nth-child("+$indx+")").prop({"selected" : this.checked});
});
})
</script>
</head>
<body>
<form id="form1" action="blank.html" method="post">
<input value="1" type="checkbox" />1<br />
<input value="2" type="checkbox" />2<br />
<input value="3" type="checkbox" />3<br />
<input value="4" type="checkbox" />4<br />
<input value="5" type="checkbox" />5<br />
<select id="select1" multiple="multiple" size="5">
<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>
</select>
</form>
</body>
</html>