Radiation-induced chromosomal rearrangement as an aid to analysis of the genetic constitution of Phaffia rhodozyma

Electrophoretic karyotypes of 80 auxotrophic and morphological mutants obtained from two Phaffia rhodozyma strains (ATCC 24203 and ATCC 24229) by γ-radiation were investigated. Contour-clamped homogeneous gel electrophoresis separation of the chromosomal size DNAs revealed 29 new chromosomal patterns after mutagen treatment. No correlation was found between a given type of chromosomal aberration and any phenotypic character. However, analysis of the chromosomal rearrangements proved to be useful for a more exact determination of chromosome number and genome size. The total genome size of ATCC 24229 was found to be 19.3 Mb, with nine chromosomes, while analysis of the mutant derivatives of ATCC 24203 suggested the presence of 11 chromosomes, with an estimated total genome size of 22.2 Mb. The advantages of the analysis of mutant electrophoretic karyotypes for genome characterization are discussed.