[Bio-Linux] Cannot install on Ubuntu "Depends: bio-linux-base-directories:i386 (>= 1.0-1) but it is not installable"

[Stephane Bortzmeyer]

I try to install biolinux on an existing Ubuntu 12.04. For several
packages, I get:

# apt-get install bio-linux-ape
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 bio-linux-ape:i386 : Depends: bio-linux-base-directories:i386 (>= 1.0-1) but it is not installable
E: Unable to correct problems, you have held broken packages.


But I have bio-linux-base-directories, and at a more recent version:

# apt-cache show bio-linux-base-directories
Package: bio-linux-base-directories
Priority: optional
Section: science
Installed-Size: 3488
Maintainer: Bela Tiwari <helpdesk at envgen.nox.ac.uk>
Architecture: all
Version: 1.0-37

I even checked the version numbers:

# if dpkg --compare-versions 1.0-37 '>=' 1.0-1; then echo OK; fi
OK

I am now completely lost. What is apt-get expecting?