Genetic dissection of clonally inherited genomes of poeciliopsis. I. Linkage analysis and preliminary assessment of deleterious gene loads.

Theoretical considerations suggest that a high load of deleterious mutations should accumulate in asexual genomes. An ideal system for testing this hypothesis occurs in the hybrid all-female fish Poeciliopsis monacha-lucida. The hybrid genotype is retained between generations by an oogenetic process that transmits only a nonrecombinant haploid monacha genome to their ova. The hybrid genotype is re-established in nature by fertilization of these monacha eggs with sperm from a sexual species, P. lucida. The unique reproductive mechanism of these hybrids allows the genetic dissection of the clonal monacha genome by forced matings with males of P. monacha. The resultant F(1) hybrids and their backcross progeny were examined to determine the amount and kinds of genetic changes that might have occurred in two clonal monacha genomes.-Using six allozyme markers, four similar linkage groups were identified in each clonal genome. Segregation and assortment at these loci revealed no apparent differences between monacha genomes from sexually and clonally reproducing species. Mortality of F(1) and backcross progeny revealed differences between the two clonal genomes, suggesting that deleterious genes may accumulate in genomes sheltered from recombination.