Mini-chromosomes from telomere-mediated chromosomal truncation of A and B chromosomes in maize. (A) Mini-chromosome R2 from the truncation of an A chromosome in a tetraploid plant. Centromere and NOR were labeled green; transgene was labeled red. Arrow denotes R2. (B) and (C) Mini-chromosomes from truncations of B chromosomes. B chromosome centromeres were labeled green; transgene was labeled red. Arrows point to mini-chromosomes. (D) and (E) Mini-chromosome as in (B) at pachynema (D) and anaphase I (E) of meiosis. B chromosome centromeres were labeled red and knobs were labeled green. Arrows denote mini-chromosomes. The pachytene chromosomes in (D) were used to measure the size of the mini-chromosome and its centromere by comparison with those of the normal B chromosome. The sister chromatids of the mini-chromosome separate at anaphase I (E). (F) Progeny of the mini-chromosome shown in (B). Two mini-chromosomes were transmitted to an F1 by the mechanism of nondisjunction when a male parent carrying the mini-chromosome was used in an outcross. B chromosome centromeres were labeled green. Arrows denote the mini-chromosomes. Scale bar = 10 microns.

Karyotype analysis of a minichromosome derived from bombardment of free telomeres and a plasmid construct that contains an endogenous A centromere. The stock was karyotyped using the following FISH probes: CentC (green), TAG (green), NOR (green), and pGZ transgene (red). The counter stain is DAPI (Blue). Transgene signal and CentC localized to a small centromere-sized chromosome (arrow). No chromosomes were missing from the normal complement of chromosomes. Scale bar = 10 microns. From Gaeta et al. 2013, Chromosoma.