Field inversion gel electrophoresis has been used to improve the resolution of the large chromosomes (greater than 1000 kb) present in Saccharomyces kluyveri and in several genera of yeasts other than Saccharomyces cerevisiae, and thus establish more accurately the electrophoretic karyotype of these yeasts. Field inversion gel electrophoresis has also been used to demonstrate the presence of chromosome length polymorphisms in several of the yeasts studied. By Southern blotting techniques the greater degree of relatedness of S. kluyveri and Kluyveromyces lactis to S. cerevisiae, as compared to that of the other genera of yeasts studied, has been established.