Transmission and recombination of extranuclear genes during sexual crosses in Aspergillus nidulans

Three extranuclear mitochondrial mutations in Aspergillus nidulans, (oliA1), (camA1) and (cs67), were used as markers in sexual crosses to provide information on the frequencies of transmission and recombination of the mitochondrial genome. Any individual perithecium contained ascospores of only one extranuclear genotype. Using mono-, bi- and trifactorial crosses it was found that all three markers could be recovered from the progeny, although the transmission frequencies were different for each marker. This bias was present irrespective of the nuclear background or the presence of selective agents in the medium on which the cross was established. These findings enable a series of “transmission strength” to be established, as shown below:- \(\begin{gathered} (camA1) > (cs67,{\text{ }}camA1) > ( + ) = (cs67) > (oliA1,cs67) \\ {\text{ }} > (oliA1) > (oliA1,{\text{ }}camA1) \\ \end{gathered} \) However, the numbers of recombinants isolated were so variable as to make this form of analysis unsuitable for mapping the mitochondrial genome.