JS Help with Interactive Map

I’ve been watching this tutorial:

Custom Interactive Maps with the Google Maps API 11 Advanced Marker Organization

I have it working, but their “remove” is done via function:

map.removeBy(function(marker) {
	return marker.id=== 2;

I want to tie this function to a select menu. So when I select something that has a value of “2”, it passes that to this function.

<select><option value="1">Section 1</option>
<option value="1">Section 1</option></select>

I have very little experience in Javascript and this is way over my head. Any help would be appreciated.