The mitochondrial genome of Chlamydomonas. II. Genetic analysis of non-mendelian obligate photautotrophic mutants.

Among a collection of obligate photoautotrophic (dark-dier, dk) mutants isolated in Chlamydomonas reinhardtii, two have been found which are inherited in crosses to wild type in a non-Mendelian, biparental and apparently random fashion. F1 progeny include not only cells which show the dk and wildtype parental phenotypes but also many which possess intermediate phenotypes between wild type and dk. When F1 progeny with dk, intermediate or wild-type phenotype were backcrossed to wild type, the dk phenotype continued to be inherited in a biparental and random fashion. Upon selection, neither mutant formed stable clones producing only dk progeny, suggesting that the two mutants segregate dk and wild-type progeny somatically and that the homozygous dk condition may be lethal. The biparental transmission of these two non-Mendelian dk mutations resembles the transmission of acriflavin-induced minute mutations of Chlamydomonas and is distinct from the uniparentally inherited chloroplast mutations of this alga. Both the dk and minute mutations may alter mitochondrial DNA and thereby alter mitochondrial functions.