Haploidization Analysis in Penicillium chrysogenum

SUMMARY: Results relevant to the problem of increasing penicillin yield in Penicillium chrysogenum by recombination through the parasexual cycle are discussed. Sister strains differing from each other in few mutational steps have been used to construct a map with three haploidization groups. By this approach it has been possible to overcome those barriers to recombination, principally chromosome rearrangements, which arise when non-sister strains are used. Selection against an allele has been demonstrated and the problem solved by use of p-fluorophenylalanine to induce haploidization. In addition, the selection of a morphologically stable strain from an unstable strain has been achieved and the genetic determinant for this instability allocated to a haploidization group.