from Lisa C. Ranford-Cartwright, Karen l. Hayton and Michael T. Ferdig writing in Malaria Parasites: Comparative Genomics, Evolution and Molecular Biology:
Experimental genetic crosses mimic the sexual reproduction process, and accompanying genetic recombination, that occurs between individuals of the same species during natural transmission. Experimental crosses performed using rodent and human species of Plasmodium have been used to link phenotype and genotype for a variety of traits, and have been particularly useful for understanding phenotypes for which no obvious candidate genes are known. In addition, analysis of experimental crosses has provided insights into the frequency and types of recombination that occur. Some biological traits are explained by inheritance of single genes, whereas several loci, known as quantitative trait loci (qtl), contribute to a "complex trait". Linkage analysis of experimental genetic crosses of Plasmodium falciparum have identified parasite loci contributing to resistance to a number of antimalarial drugs such as chloroquine and quinine, as well as loci controlling the ability of parasites to invade erythrocytes of different primate species, the ability to infect mosquitoes, and intraerythrocytic growth rates. Genetic mapping can also identify genomic regions associated with the control of gene expression (expression qtl or eQTL). Genetic crosses and genetic mapping continue to play a significant role in our understanding of malaria parasite biology, transmission, and drug resistance.
Further reading: Malaria Parasites: Comparative Genomics, Evolution and Molecular Biology