I don't think that the minor version will be mixed. This is why I wrote in a prev. post here to list /usr/bin/ for example. During the installation, a separate folder is created for each version. I remember that this happened to me once when I installed another Python version in addition to the standard major versions which come with the system. If you have installed python2.7 and python3.6 there will be folders in /usr/bin/ with the same names. If you install python3.5 the corresponding directory will appear along the others. I will try it later on my Arch.
Then you create the environment pointing to the exact version you want:
$ virtualenv -p /usr/bin/python3.5/python3.5 my_3.5_env
If you have anaconda installed you can point to its python version
$ virtualenv -p /home/$USER/anaconda/bin/python
For example.
Doesn't matter if you install any python version you want. Mixing is impossible. Let say you have installed 2.6, 2.7, 3.4, 3.5 and 3.6.
In .bashrc you just create an alias for each version:
# .bashrc
....
....
# another content
alias p2.6="/usr/bin/python2.6/python2.6"
alias p2.7="/ust/bin/python2.7/python2.7"
alias p3.4="/usr/bin/python3.4/python3.4"
alias p3.5="/usr/bin/python3.5/python3.5"
alias p3.6="/usr/bin/python3.6/python3.6"
Then you can install
virtualenvwrapper and do something like:
$ mkvirtualenv -p p3.4 my_3.4_env
Anyway, I've never used this.