A Cytophotometric Investigation of Haploid × Polyploid Matings in the Acellular Slime MoldDidymium Iridis

Abstract

SUMMARY -Feulgen-DNA cytophotometry has been used to analyze matings between compatible haploid and polyploid myxamoebae of the plasmodial slime mould Didymium iridis. The polyploid myxamoebae used in this investigation included both a naturally occurring isolate and three isolates which had been induced to become polyploids by treating the parental haploid isolates with the mitotic inhibitor isopropyl N-(3-chlorophenyl) carbamate (CIPC). Regardless of the source of the polyploid parent, the maximum frequency of heterokaryon formation attained was approximately 40 percent; however, the frequency at which the heterokaryons were converted to zygotes was substantially lower in the case of the CIPC-induced polyploids than it was with the naturally occurring polyploid isolate. With the naturally occurring polyploid the maximum frequency of zygote formation was 32 percent, whereas the maximum frequency of zygote formation varied from 10 to 18 percent with the CIPC-induced polyploids. On the basis of these experiments we are able to conclude that polyploidy does not form a barrier to syngamy between myxamoebae which bear compatible mating alleles and that the aberrant mating results which have been previously observed to result from crosses between haploid and polyploid isolates are most likely attributable to chromosome eliminations which follow syngamy and zygote formation.