Debian/Apt inquiry

Have a quick question.... I have Mepis 3.3.3 and often use apt to upgrade apps; ie

$ apt-get clean
$ apt-get update
$ apt-get upgrade

All works well, my question is, will it do a major upgrade? For example I have php 4.4.0-4, will it ever goto php 5? Same w/MySQL, its ver 4.1.15, will it go to MySQL 5? As of now it keeps php and mysql as ver 4.x.x.x. I am only using these 2 as examples.

And my /etc/apt/source.list is one from Mepis Lovers.

Thanks,
Travis