Uniparental inheritance of organelle genes C. William Birky  Current Biology  Volume 18, Issue 16, Pages R692-R695 (August 2008) DOI: 10.1016/j.cub.2008.06.049 Copyright © 2008 Elsevier Ltd Terms and Conditions

Figure 1 Selective silencing of chloroplast DNA in Chlamydomonas. A zygote was stained with SYBR Green 1 and examined with a UV fluorescence microscope; chlorophyll autofluoresces red while the stained DNA is yellow. The original mt+ and mt− cells form the left and right halves of the zygote, respectively. Top: before selective silencing, large aggregates of cpDNA (nucleoids) are seen in the unfused chloroplasts. Bottom: 10 minutes later the nucleoids in the mt− chloroplast have been completely digested. Photographs courtesy of Yoshiki Nishimura (University of Tokyo). Current Biology 2008 18, R692-R695DOI: (10.1016/j.cub.2008.06.049) Copyright © 2008 Elsevier Ltd Terms and Conditions

Figure 2 Illustration of a yeast cross between strains with erythromycin resistant (eryr) mitochondrial genomes (red) and erythromycin sensitive (erys) genomes (blue). Haploid cells of the two genotypes are mixed (top) and fuse in pairs to form zygotes, all of which are heteroplasmic (have two alleles of a mitochondrial gene). Individual zygotes are isolated and allowed to produce zygote clones in which every cell is homoplasmic resistant or sensitive as a result of vegetative segregation. (Real zygote clones contain ≥1000 cells.) Illustrated are uniparental zygotes with 0 or 100% eryr cells and genomes, as well as biparental zygotes with 20% and 70% resistant genomes. At bottom is a frequency distribution of the mitochondrial gene frequencies in zygote clones. Note that if one analyzed a sample of progeny from the cross without first isolating zygotes, one would not detect uniparental zygotes. Data from Thrailkill, K., Birky, C. William Jr., Luckemann, G., and Wolf, K. (1980) Intracellular population genetics: Evidence for random drift of mitochondrial allele frequencies in Saccharomyces cerevisiae and Schizosaccharomyces pombe. Genetics 96, 237–262; with permission from the Genetics Society of America. Current Biology 2008 18, R692-R695DOI: (10.1016/j.cub.2008.06.049) Copyright © 2008 Elsevier Ltd Terms and Conditions