DNA HOMOLOGIES AMONG HOMOTHALLIC, PSEUDO-HOMOTHALLIC AND HETEROTHALLIC SPECIES OF NEUROSPORA

Highly purified DNA from 3 homothallic species N. africana, N. dodgei and N. lineolata; 3 reference strains representing authentic heterothallic species, N. crassa, N. intermedia and N. sitophila; and 2 strains of pseudo-homothallic species N. tetrasperma were characterized by spectrophotometry and DNA reassociation using hydroxyapatite chromatography. All of these known species are closely related on the basis of DNA characteristics such as base composition and thermal denaturation profiles of major DNA components. Minor components of ascospore DNA was, however, only 5-7% of total DNA instead of 15-20% minor component DNA shown by mycelial DNA. Species belonging to the same group were not distinguishable morphologically, but all of these species were distinguishable by DNA:DNA homology studies. Greater DNA homology was noticed between DNAs of heterothallic species and DNAs of pseudohomothallic species than DNA of true homothallic species. Difference on DNA-nucleotide sequences among homothallic species was very little. Pseudo-homothallic species N. tetrasperma was found to be distinctly different from homothallic species but closer to heterothallic species based on such studies.