Radio button validation in javascript check or uncheck

Radio button validation in javascript check or uncheck

<form action="" method="post" name="register_form" id="register_form" enctype="multipart/form-data">

    <div class="text-input">
        <label>Gender: </label>
        <input class="form-control" type="radio" name="gender" id="male" value="male" />
        <label for="male">Male</label>
        <input class="form-control" type="radio" name="gender" id="female" value="female" />
        <label for="female">Female</label>
    </div>
    <div class="text-input" align="center">
        <input type="submit" name="register" value="Submit" onclick="return radioValidation();" />
    </div>

</form>

<script type="text/javascript">
function radioValidation(){

var gender = document.getElementsByName('gender');
var genValue = false;

for(var i=0; i<gender.length;i++){
if(gender[i].checked == true){
genValue = true;
}
}
if(!genValue){
alert("Please Choose the gender");
return false;
}

}
</script>