INTERCHROMOSOMAL EXCHANGE OF A LARGE SUBTELOMERIC SEGMENT IN A PLASMODIUM-FALCIPARUM CROSS

Duplications and interchromosomal transpositions of chromosome segment s are implicated in the genetic variability of Plasmodium falciparum m alaria parasites. One parasite clone, HB3, was shown to lack a subtelo meric region of chromosome 13 that normally carries a PfHRPIII gene. W e show here that the chromosome 13 segment carrying PfHRPIII was repla ced in HB3 by a duplicated terminal segment from chromosome 11. Mappin g results indicate that the segment includes at least 100-200 kb of su btelomeric DNA and contains duplicated copies of the Pf332 and RESA-2 genes. We followed inheritance of this duplication in a genetic cross between the HB3 and another P.falciparum clone, Dd2, that is euploid f or the Pf332, RESA-2 and PfHRPIII genes. Three types of progeny from t he cross showed expected inheritance forms: a Dd2 euploid parent type, an HB3 aneuploid parent type, and a recombinant euploid type that car ried PfHRPIII from Dd2 chromosome 13 and Pf332 from HB3 chromosome 11. However, a fourth euploid progeny type was also observed, in which th e chromosome 13 segment from HB3 was transposed back to replace the te rminus of chromosome 11. Three of 14 individual progeny were of this t ype. These findings suggest a mechanism of recombination from subtelom eric pairing and exchange between non-homologous chromosomes in meiosi s.