Nucleolar dominance in interspecific hybrid of Fuchsia

Abstract

The occurrence of nucleolar dominance has been recorded in many interspecific hybrids where in the rRNA genes inherited from one of the parents are transcribed and those derived from the other parent are silent. In a total of 125 cross combinations attempted by interspecific hybridization in Fuchsia, this phenomenon was observed in the interspecific hybrid (2n=22) between F. triphylla and F. arborescens during the cytogenetic studies carried out using root tip squash technique, air dried chromosome spreads, and silver staining of Nucleolar Organizer Regions (NORs). In this interspecific hybrid, only one chromosome expressed the secondary constriction derived from one of its parental species at mitotic metaphase. It is presumed that NOR of F. triphylla with the genome size of 1643 Mbp might have failed to display its secondary constriction and was suppressed by F. arborescens with genome size of 1594 Mbp as underdominant rRNA genes in the plant hybrids present from the larger genome of the parental species, rich in repetitive DNA in heterochromatin.