Physical evidence for recombination of chloroplast dna in hybrid progeny of Chlamydomonas eugametos and C. moewusii.

Differences in the restriction endonuclease fragmentation patterns of chloroplast DNA (cpDNA) from C. eugametos and C. moewusii have been used to study the inheritance of these DNAs in interspecific hybrids. Analysis of the cpDNAs from ten randomly selected F1 hybrids, in each case revealed cpDNA to be recombinant for AvaI and BstEII restriction sites, although fragments characteristic of C. eugametos, the mt+ parent, were typically found in excess of those for C. moewusii, the mt- parent. In backcrosses between an F 1 mt+ hybrid and C. moewusii mt-, seven randomly selected B1 hybrids showed cpDNA restriction patterns either identical to or highly similar to that of the mt+ parent. We propose that cpDNA molecules are predominantly transmitted by the mt+ parent in both F1 and B1 generations but that selection favors survival of F1 progeny with recombinant chloroplast genomes which avoid interspecific incompatibilities. On the surface, the inheritance of recombinant cpDNA contrasts with the simultaneous uniparental inheritance of two putative chloroplast markers (sr-2 and er-nM1 (+)). However, it may be that these two markers are by chance associated with cpDNA sequences of the mt+ parent which were selected in all F1 hybrids.