将动态创建的下拉列表中的变量传递给Php以在同一页面上的Div中运行和显示

I've searched through StackOverflow as well as multiple other sites but have not found a way to make this work as per the title. I have a base page that has a dropdown list automatically created as below:

<div class="tipfixtures">
    <div class='styled-select blue semi-square'>
        <select id="selFixRounds" onchange="getFixtureRound();">
            <?php for ($x = 1; $x <= $compRounds; $x++) {
                echo "<option value=".$x.">Round ".$x."</a>";
            } ?>
        </select>
    </div>
</div>
<div id='rndList'>
    <?php include ('fixtureTable.php'); ?>
</div> 

The dropdown works fine and from this list I can select an entry, the following query assigns the value of the selected entry to fixtureRound:

    function getFixtureRound() {
        var fixRnd = document.getElementById("selFixRounds");
        var fixtureRound = fixRnd.options[fixRnd.selectedIndex].value;
        $.ajax({
            url: 'fixtureTable.php',
            type: 'GET',
            data: ({fixtureRound}),
        })
    }

It is supposed to pass the fixtureRound value back to the query in fixtureTable.php as fixtureTable.php?fixtureRound=number via AJAX. I've checked the console headers and the url shows as it should above and the params showing fixtureRound: number. However I cannot get fixtureTable to recognise the GET variable, have the following code in the fixtureTable.php file:

$round = $_GET['fixtureRound'];

But am getting an undefined variable error plus I am unsure how to get the php to display. Any help greatly appreciated as I'm probably missing something really obvious here!

** EDIT ** Ok so I've dialled back the dumb a tad and have added isset for the $_GET which has gotten rid of the undefined error plus it now showing the correct listings in the console - Response Preview & Payload whenever different selections are made in the dropdown menu showing fixtureTable.php is being run with the correct $round variable, however it is not displaying the correct results in the div.

Solved the last part of the problem by actually outputting fixtureTable.php in the rndList div using the success condition in the AJAX code. Here is the script code in full:

function getFixtureRound() {
var fixRnd = document.getElementById("selFixRounds");
var fixtureRound = fixRnd.options[fixRnd.selectedIndex].value;
    $.ajax({
        url: 'fixtureTable.php',
        type: 'GET',
        data: ({fixtureRound}),
        success: function(response) {
            $("#rndList").html(response);
        }
    }) 
}