Here's Javascript that you should be able to easily adapt to your specific elements:
$('#dropdownlist').on('change', function () {
if ($(this).val()) {
if($(this).val() === "some value") {
$('#somecheckboxgroup').show();
$('#someothercheckboxgroup').hide();
}
else if($(this).val() === "some other value") {
$('#somecheckboxgroup').hide();
$('#someothercheckboxgroup').show();
}
}
});
Essentially, you just want to run a function every time the dropdownlist changes, and in it, check the currently selected value and then run your desired code based on the observed value.