Genetic Crosses in the Apicomplexan Parasite Cryptosporidium Parvum Define Recombination Parameters

Recombinant progeny lines of Cryptosporidium parvum were generated by coinfecting immunosuppressed mice with two genetically distinct isolates of C. parvum. Progeny lines were obtained from a cross of parental lines MD x TU114 through targeted propagation in mice of progeny oocysts originating from populations lacking one parental allele at one or more loci. For each infection lineage this process was repeated until only a single allele remained for each marker, indicating that the progeny line was clonal. To study genetic recombination, 16 progeny clones were genotyped at 40 loci located on each of the eight chromosomes. The inheritance of parental alleles was significantly skewed towards the more virulent parent isolate MD. A contiguous 476 kb segment of chromosome V displayed MD allele in all progeny recovered, while MD and TU114 alleles were detected at other loci throughout the genome. The absence of alleles from one parental isolate in this chromosomal region may indicate phenotypic selection for the MD allele during the generation of these lines. A range for the meiotic crossover frequency was determined on the basis of 40 markers and the number of meioses estimated to have taken place during the crossing experiment. C. parvum exhibits a high rate of recombination commensurate with other Apicomplexa.