A SEX DETERMINING MECHANISM IN THE CLOSTERIUM-EHRENBERGII (CHLOROPHYTA) SPECIES COMPLEX

Homozygous mt−/mt− diploid clones of the Closterium ehrenbergii Menegh. ex Ralfs species complex were obtained by hypertonic treatment from minus vegetative cells, and mating type segregation ratios in the F1 progeny of “triploid” zygospores between wild type mt+ haploid and mt−/mt− homozygous diploui were analyzed. The ratio of plus to minus individuals was 1:4.8, and the ratio of the pairs of opposite mating types to those of minus mating type was 1:2.1. The results clearly show that mt− is dominant to mt+ and that the mating type inheritance in these zygospores follows the triploid‐like pattern. The validity of our assumption that the two mating types are determined by one genetic factor (mt− allele dominant) was confirmed in B1 progeny analyses as well. The results suggest that this sex determining mechanism is working effectively in the C. ehrenbergii species complex, in which several biological species have evolved through polyploidization. Copyright © 1990, Wiley Blackwell. All rights reserved