RESUMEN
The inheritance of both the mitochondrial DNA (mtDNA) and the nuclear-encoded extrachromosomal ribosomal DNA (rDNA) has been studied in the myxomycete, Didymium iridis, by DNA-DNA hybridization of labeled probes to total DNA at various stages of the life cycle. Both the mtDNA and rDNA populations rapidly become homogeneous in individuals, but there is a qualitative difference in the patterns of inheritance of these two molecules. One parental rDNA type was preferentially inherited in all crosses; selective replication of this molecule is tentatively proposed as the mechanism of inheritance. In contrast, either parental mtDNA type could be inherited. Since the inherited population of parental mtDNA molecules are not partitioned into cells in this coenocytic organism, no known mechanism of inheritance can explain the rapid and apparently random loss of one parental mtDNA type in individuals.
Asunto(s)
ADN de Hongos/genética , Herencia Extracromosómica , Mixomicetos/genética , Clonación Molecular , ADN Mitocondrial/genética , ADN Ribosómico/genética , Haploidia , Mixomicetos/crecimiento & desarrollo , CigotoRESUMEN
Incompatibility reactions of somatic cells in the myxomycete Didymium iridis are controlled by several loci displaying simple dominance. Phenotypically dissimilar plasmodia generally undergo a temporary fusion which is quickly terminated by a cytotoxic reaction, whereas phenotypically similar ones undergo fusion which is not followed by such reactions. The size of the killed areas varies from microscopic up to a few square centimeters and is directly correlated with the amount of protoplasmic mixing which occurs. The amount of mixing itself is controlled by the incompatibility loci through regulation of the speed of killing. Each locus allows a characteristic amount of mixing and when two or more loci act together the amount is reduced by a subtractive effect. This results in a smaller killed area because of the more rapid cytotoxic reaction. Such a reaction is also unidirectional for each locus, with killing taking place in the recessive phenotype. Reversion of some heterokaryons to a homokaryotic state within 24 hours is considered evidence for the existence of unidentified weak incompatibility loci which act very slowly.
RESUMEN
Plasmodial (somatic) fusion in a strain of Physarum polycephalum, a true slime mold, is controlled by four loci, each of which displays simple dominance. Two diploid plasmodia fuse with each other only if they are phenotypically or genotypically identical for all four fusion loci.
