[php] Php - testing if a radio button is selected and get the value

my form:

<form method="post" action="radio.php">
   select your gender: 
    <input type="radio" name="radioGender" value="female">
    <input type="radio" name="radioGender" value="male">
    <input type="submit" name="btnSubmit" value="submit">
</form>

my php:

   <?php
      if (isset($_POST["btnSubmit"])) {
        if (isset($_POST["radioGender"])) {
        $answer = $_POST['radioGender'];
           if ($answer == "female") {
               echo "female";
           } else {
               echo "male";
           }    
        }else{
            echo "please select your gender";
             }
      }
  ?>