We have written a BASIC program about survival and heterokaryosis in Phycomyces for APPLE II series. Surviving and heterokaryotic unit fraction of spores as a consequence of several lethal effects such as mitotic, dominant and recessive lethals can be computed by the system, and also the uninucleate fraction of spores which were originated by mitotic and recessive lethals.The probability of a mitotic lethal per nucleus can be also computed starting from the only surviving unit fraction of spores The program can also compute the relationship between the mutation rates due to mitotic and recessive lethals acting together concurrently, introducing surviving and heterokaryotic unit fraction of sporesThe program can be easily modified to run on different microcomputers with similar versions of BASIC