Molecular karyotype of Plasmodium falciparum: conserved linkage groups and expendable histidine-rich protein genes.

We describe fractionation of the Plasmodium falciparum genome into 14 chromosomal DNA molecules by pulsed-field gel electrophoresis. This number agrees with the number of chromosomes observed by electron microscopic visualization of kinetochores. The assignment of 25 markers to 12 of the 14 chromosomes in three cloned parasite lines demonstrates that chromosomal size variation can greatly change the relative migration of genetically equivalent chromosomes. Deletions that include genes for three different histidine-rich proteins, located on chromosomes 2, 8, and 13, contribute to size differences in some clones. Other karyotypic differences result from chromosome segregation and/or recombination during meiosis.