title: Nature of B chromosomes in the harvest mouse Reithrodontomys megalotis by fluorescence in situ hybridization (FISH).
abstract: Using fluorescence in situ hybridization, we examined the characteristics of two types of B chromosomes in harvest mice of the genus Reithrodontomys. B chromosomes were interrogated with rDNA, telomeric repeat, LINE element and centromeric heterochromatin probes. The two types of B chromosomes share the following features: (a) telomeres present on the ends of both arms; (b) hybridization to LINE probes; (c) absence of hybridization to the ribosomal gene probes; (d) C-band-positive centromeric regions; and (e) euchromatic arms. They differ as follows: (a) the larger B element hybridizes to the centromeric heterochromatin (pMeg-1) probe whereas the smaller B element does not; (b) the amount of C-band-positive material is reduced in the smaller B chromosome relative to that present on the larger B chromosome; and (c) the smaller element is reduced in size by about a third. It is concluded that the larger B chromosome arose as a leftover centromere from centric fusion, whereas the smaller element has a different origin perhaps as an intact fragment or as an amplified region from the A chromosomes. The presence of euchromatic regions on B chromosomes may account for their survival in the karyotype.
authors.affiliation: Department of Biological Sciences, Texas Tech University, Lubbock 97409-3131, USA. bjjap@ttacs.ttu.edu
authors.forename: J A
authors.initials: JA
authors.lastname: Peppers
authors.forename: L E
authors.initials: LE
authors.lastname: Wiggins
authors.forename: R J
authors.initials: RJ
authors.lastname: Baker
mesh_terms: D000818:Animals; D002503:Centromere / Q000235:genetics; D002875:Chromosomes / Q000235:genetics*; D015342:DNA Probes / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D006570:Heterochromatin / Q000235:genetics; D017404:In Situ Hybridization, Fluorescence; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics; D016205:Sigmodontinae / Q000235:genetics*; D016615:Telomere
chemical_list: D015342:DNA Probes; D004251:DNA Transposable Elements; D004275:DNA, Ribosomal; D006570:Heterochromatin