High amount of heterochromatin in a tropical tree species: Genipa americana L. (rubiaceae).

Abstract

The chromosomes and interphase nuclei of Genipa americana L. were analyzed after CMA/DAPI staining. Most of the large chromocentres was CMA+/DAPI+, except that associated with the nucleolus which was CMA + +/DAPI - -, whilst the diffuse euchromatin was CMA-/DAPI+. In addition, some small chromocentres were CMA-/DAPI+. The chromosome bands were CMA +/DAPI + or CMA + +/DAPI- -. Most of the chromosome pairs showed size heteromorphism, mainly in the CMA+/DAPI+ bands. Measurements of the heterochromatin/euchromatin ratio in metaphase chromosomes gave an estimate of about 50%, one of the highest ratio observed in angiosperms. Comparison with some other species with a high heterochromatin amount suggest that heterochromatin accumulation may be an aleatory rather than an adaptive process. © 1993, Japan Mendel Society, International Society of Cytology. All rights reserved.