Here's hoping you have your iTunes showing the same views as mine (it is so customizable now)....
When you are in iTunes, be in the Apps tab (click the button on the top left; select Apps in the drop down). On the right side, across the top, is a title line. One of the lines should be titled "List." Click on that and you will get a columnized list. One of the columns is Genre and, if you click on the word Genre, it will sort them for you.
I can't find any way to sort them by genre when you are in the All category (where you can see the icons); that appears to be alphabetical only. Sorry.
Still - I hope this helps.
Marilyn