Genetic crosses within and between species of Cryptosporidium .

can recombine their genomes through sex. The progeny of such genetic crosses shows combined features of both parents, with resistance to multiple drugs being one example. Sex thus provides a critical mechanism for the parasite to rapidly adapt to changing environments and hosts. Genetic crosses as an experimental tool may also be harnessed in the future to discover the genes underlying differences in virulence, drug sensitivity, and immunogenicity between parasite isolates.