An apr file extension is related to the SAM (Sequence Alignment and Modeling system) and used for its alignment probabilities files.
.APR file extension - SAM alignment probabilities
What is apr file? How to open apr files?
File type specification:
The apr file extension is used for SAM (Sequence Alignment and Modeling system) alignment probabilities file, as created by pathprobs. An RDB-compatible format.
Most likely some old format without support. No further information could be found.
This apr file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.
The default software associated to open apr file:
Sequence Alignment and Modeling system 
Company or developer:
Richard Hughey - Kevin Karplus - Anders Krogh
Sequence Alignment and Modeling system (SAM) is a collection of fsoftware tools for creating, refining, and using linear hidden Markov models for biological sequence analysis.
The model states can be viewed as representing the sequence of columns in a multiple sequence alignment, with provisions for arbitrary position-dependent insertions and deletions in each sequence. The models are trained on a family of protein or nucleic acid sequences using an expectation-maximization algorithm and a variety of algorithmic heuristics. A trained model can then be used to both generate multiple alignments and search databases for new members of the family.
List of software applications associated to the .apr file extension
Recommended software programs are sorted by OS platform (Windows, macOS, Linux, iOS, Android etc.)
and possible program actions that can be done with the file: like open apr file, edit apr file, convert apr file, view apr file, play apr file etc. (if exist software for corresponding action in File-Extensions.org's database).
Hint:
Click on the tab below to simply browse between the application actions, to quickly get a list of recommended software, which is able to perform the specified software action, such as opening, editing or converting apr files.
Settings file type for software that use apr file - SAM alignment probabilities
Programs supporting the exension apr on the main platforms Windows, Mac, Linux or mobile. Click on the link to get more information about Sequence Alignment and Modeling system for settings apr file action.
