A genetic linkage map of the apicomplexan protozoan parasite Eimeria tenella

Apicomplexan protozoan parasites have complex Life cycles that involve phas es of asexual and sexual reproduction. Some genera have intermediate insect hosts, For example, Plasmodium spp. (the cause of malaria), but related ge nera such as Eimeria spp. (causative agents of coccidiosis in poultry) have a direct life cycle occurring in only a single host. Mechanisms that regul ate the life cycles of apicomplexan parasites are unknown, but the intracel lular growth of avian Eimeria spp. is easily shortened by serial selection for the first parasites to complete the transition from asexual to sexual r eproduction (to yield so-called precocious lines). To investigate the genet ic basis of such an abbreviated life cycle, we have used the species E. ten ella and analyzed the inheritance of 443 polymorphic DNA markers in 22 reco mbinant cloned progeny derived from a cross between parents that had select able phenotypes of precocious development or resistance to an anticoccidial drug. The markers were placed in 16 linkage groups (which defined 12 chrom osomes) and a further 57 unlinked groups. Two linkage groups showed an asso ciation (P=.0105) with the traits of precocious development or drug-resista nce and were mapped to chromosome 2 (ca 1.2 Mbp) and chromosome 1 (ca 1.0 M bp), respectively. The map provides a framework for further studies on the identification of genetic loci implicated in the regulation of the life cyc le of an important protozoan parasite and a representative of a major taxon omic group.