RDNA SITES AND HETEROCHROMATIN IN MEIWA KUMQUAT (FORTUNELLA-CRASSIFOLIA SWING.) CHROMOSOMES REVEALED BY FISH AND CMA DAPI STAINING/

Fluorescence in situ hybridization (FISH) was used to localize rDNA si tes in relation to heterochromatic regions revealed by double chromomy cin A(3) (CMA) and 4'-6-diamidino-2-phenylindole (DAPI) in somatic chr omosomes of Meiwa kumquat (Fortunella crassifolia Swing.). Four sites were observed, all corresponding to CMA positive regions. Two of them were located in the centromeric region of the two chromosomes with thr ee CMA bands (type A chromosome), and the other two, in the long arm's terminal region of the chromosomes with terminal CMA bands on both te lomeres (type C). These sites were of different sizes among probable h omologous chromosomes, most likely due to a hybrid origin of this acce ssion. The sites located in the type C chromosomes represent a new loc us of rRNA genes in these taxa, suggesting that different evolutionary pathways may lead to a similar heterochromatin distribution, and, hen ce, that chromosomes with the same CMA banding pattern among different species may not always be homoeologous.