Highly polymorphic ISSR-PCR markers, the DNA fragments flanked by invert microsatellite repeats, are widely applied with the aim of the genomic scan (polyloci genotyping). The sequencing of such DNA fragments from domestic horse and cattle genomes testified the close connection between the inverted microsatellite repeats and products of recombination between endogenous retroviruses. Mutual genomic positioning of microsatellites and endogenous retroviruses as a source of polymorphisms of ISSR-PCR markers was discussed.