Biased and non-biased transmission of chloroplast genes in somatic fusion products of Chlamydomonas reinhardtii.

The mode of chloroplast gene inheritance in the somatic fusion products of Chlamydomonas reinhardtii was studied. Polyethylene glycol-induced fusion was made between vegetative or gametic cells of the same or of opposite mating type after the cell walls had been removed using the lytic enzyme prepared from mating medium. The results demonstrated that the chloroplast gene transmission patterns in the fusion products at various combinations can be divided into two types; a biased and non-biased transmission. The biased transmission in favor of the mt (+) (maternal) chloroplast genomes was observed only when mt (+) gamete had been fused artificially with m (-) gamete. The polarized transmission was not changed significantly by fusing two mating type gametes after deflagellation. Furthermore, the pattern was quite similar to that seen in the vegetative zygotes obtained by sexual cross. Nonbiased transmission was seen in the fusion products obtained by all other combinations. In these cases, the chloroplast genes from both parents were transmitted to the progeny in roughly equal frequency. The results indicate that the preferential elimination of paternal (mt (-)) chloroplast alleles that leads to the maternal inheritance depends upon the fusion of two gametes heterozygous at the mating type locus.