Hidden deleterious genetic factors affecting post‐meiotic viability in zygospore progeny of a unicellular haplontic alga, mating group A of the Closterium ehrenbergii species complex (Chlorophyta)

SUMMARY In a haplontic green alga, mating group A of the Closterium ehrenbergii Meneghini ex Ralfs species complex, viability of meiotic progeny was studied by isolating two gone cells from a single germinating zygospore. In F 1 progeny of a cross between mating‐type plus M‐16‐4a and mating‐type minus M‐16‐4b, studied in six independent experiments, percentage survivals varied little from 86 to 96 with a mean of 93 ± 1.4 SE. In F 2 progenies of crosses among eight mating‐type plus and eight mating‐type minus F 1 clones of the M‐16‐4a · M‐16‐4b cross, percentage survival varied considerably from 24 to 100, with a mean of 70.8 ± 2.2. In B 1 progenies of the above eight mating‐type plus F 1 clones, survival values were significantly different between backcrosses to the recurrent M‐16‐4b (range = 32–83, mean ± SE = 58.3 ± 6.8) and backcrosses to a genetically unrelated mating‐type minus, R‐13‐20, (85–97, 92 ± 1.6). Also in B 1 progenies of the above mating‐type minus F 1 clones, survival values were significantly different between backcrosses to the recurrent M‐16‐4a (56–90, 68.3 ± 4,4) and backcrosses to a genetically unrelated mating‐type plus, R‐13‐131 (78–93, 86.1 ± 1.6). Clearly, viabilities of meiotic progeny differed considerably between outbreedings (M‐16‐4a × M‐16‐4b, and F, clones × R‐13‐20 or R‐13‐131) and inbreedings (F 2 and F 1 clones × M‐16‐4a, or M‐16‐4b). These data suggest the presence of hidden deleterious genetic factors that may reduce viability of zygospore progeny if inbred between a pair of wild‐type strains from the normally outbreeding mating group A of the C. ehrenbergii species complex.