title: Cytomolecular characterization and origin of de novo formed maize B chromosome variants.
abstract: B chromosomes are dispensable elements that occur in many species, including maize. The maize B chromosome is acrocentric and highly heterochromatic and undergoes nondisjunction during the second pollen mitosis. In this study, we determined the genetic behavior and organization of two naturally occurring B chromosome variants (designated B(ta) and B(tb)). The morphology and genetic behavior of the B(ta) chromosome were similar to those of the typical B chromosome, but the B(ta) chromosome contained a deletion in the first heterochromatin region and had higher transmission frequencies through both male and female parents. The B(tb) chromosome was reduced in size, consisted primarily of heterochromatin, and had a lower transmission frequency. The B(tb) chromosome lacked nondisjunctional behavior, which was restored by the presence of normal B chromosomes in the cell. Furthermore, the B(tb) chromosome contained two centromeric regions, only one of which was active. The organization of these two naturally occurring B chromosome variants was also determined using fluorescence in situ hybridization with B-associated sequences and by amplification of B-specific molecular markers to create possible evolutionary models.
authors.affiliation: Department of Agronomy, National Chung Hsing University, 250 Kuo Kuang Road, Taichung, 402, Taiwan. ymcheng@dragon.nchu.edu.tw.
authors.forename: Ya-Ming
authors.initials: YM
authors.lastname: Cheng
authors.affiliation: Department of Agronomy, National Chung Hsing University, 250 Kuo Kuang Road, Taichung, 402, Taiwan.
authors.forename: Ying-Ru
authors.initials: YR
authors.lastname: Feng
authors.affiliation: Agricultural Biotechnology Research Center, Academia Sinica, Taipei, Taiwan.
authors.forename: Yao-Pin
authors.initials: YP
authors.lastname: Lin
authors.affiliation: Department of Biological Science and Technology, China Medical University, Taichung, Taiwan.
authors.forename: Shu-Fen
authors.initials: SF
authors.lastname: Peng
mesh_terms: D002460:Cell Line; D002503:Centromere / Q000235:genetics*; D032461:Chromosomes, Plant / Q000235:genetics*; D005819:Genetic Markers / Q000235:genetics; D014644:Genetic Variation; D006570:Heterochromatin / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D020071:Interspersed Repetitive Sequences / Q000235:genetics; D020161:Physical Chromosome Mapping; D003313:Zea mays / Q000235:genetics*
chemical_list: D005819:Genetic Markers; D006570:Heterochromatin
keywords: B chromosome; FISH; centromere; dicentric; maize; variant