How to fire onchange event of combobox?

I have a combobox, How to fire onchange event of the combobox and get a selected value from it.

Here is the Code what i did till now :

<select name="g1" id="select_g1">
        <option value="one">one</option>
        <option value="two">two</option>
        <option value="three">three</option>
    </select>

    <script>
        $(document).ready(function(){

            $("select_g1").change(function(){
                alert("Handled"); // alert is not fired up ...
            });
        });

    </script>

EDIT : What if i have more than one combobox :

<select name="g2">
<option value="one">one</option>
<option value="two">two</option>
<option value="three">three</option>
</select>

Also disable the value selected in combobox g1 in combobox g2.

Could anyone please tell me what is wrong with the code.

Rather than trying to use the .change event, please try to use the .on event.

You can try to use it as such:

$('#select_g1').on('change', function (e) {
    var optionSelected = $("option:selected", this);
    var valueSelected = this.value;
    alert(valueSelected);
});

See this here -> http://jsfiddle.net/ocrozmkn/

EDIT :

With respect to your edited question, you can try the following jQuery :

$('select').on('change', function (e) {
    $('select option').prop('disabled', false);
    var optionSelected = $("option:selected", this);
    var valueSelected = this.value;    
    alert(valueSelected);
    $("select option:contains('" + valueSelected + "')").attr("disabled","disabled");
});

See this here ->http://jsfiddle.net/ocrozmkn/1/

Demo for multiple comboboxes

See here -> http://jsfiddle.net/ocrozmkn/6/

Hope this helps!!!