Chromosome organisation in the Australian plague locust Chortoicetes terminifera: 2. Banding variants of the B-chromosome

B chromosomes in plants

This review of supernumerary B chromosome systems in flowering plants deals mainly with work published in the last 15 yr, hut also includes older material which has not hitherto been presented systematically. The term B chromosome (B) is defined, and there is an introductory overview dealing with general characteristics and the significance of Bs as a widespread chromosome polymorphism. Detailed sections are then presented covering the occurrence of Bs in different taxa, their structure and molecular organization, their irregular modes of inheritance, their phenotypic effects, population dynamics and origin. Particular attention is paid to the research growth points in molecular analysis of the structure and genome organization of Bs, and to transmission genotypes in the context of their adaptive versus their selfish properties. Where appropriate, reference is also made to likely future lines of research, and also to the usefulness of B chromosomes in genetic analysis and as model systems to study general phenomena of genome organization and evolution, nuclear physiology and architecture, chromosome polymorphism and selfish DNA. CONTENTS Summary 411 I. Introduction 411 II. Occurrence 411 III. Structure and organization 415 IV. Inheritance 422 V. Phenotypic effects 426 VI. Populations 429 VII. Applications 430 VIII. Origin 430 Acknowiedgements 430 References 431.

Non C-banding variants in some normal families might be homogeneously staining regions

Three families are reported showing transmission of a previously described variant, which is not associated with any clinical abnormality. The variant involves additional material at the band 9p12, which shows homogeneous staining of intermediate density with GTL- and RBG-banding, and negative staining with CBG-banding. The region stains positively with Feulgen stain. In situ hybridization with total genomic human DNA, cloned alpha satellite, satellite III, and ribosomal DNA all show no hybridization to the 9p12 variant. Two members of one of the families show the largest 9p12 variant yet reported; two other carriers in this family have inherited a variant of decreased size. It is suggested that the 9p12 variants are homogeneously staining regions. Using the ISCN three-letter convention, this variant could be described as hsr(9)(p12).

C, Q and H-banding in the analysis of Y chromosome rearrangements in Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae)

In Lucilia cuprina C-banding produces procentric bands on all autosomes and deep staining over most of the X and Y chromosomes which conciderably facilitates the analysis of complex Y chromosome rearrangements. The Y chromosome is generally darkly C-banded throughout while in the X chromosome a pale staining segment is found in the distal portion of the long arm. Modulation of the banding reaction results in 'grey' areas in both X and Y. When C-banding is compared with allocycly it is clear that not all heteropycnotic regions in the sex chromosomes C-band to the same extent. Secondary constrictions in the short arms of both X and Y chromosomes are clearly revealed by C-banding, the X satellite being polymorphic for size.--Q-banding results in a brightly fluorescing band in the short arm of structurally normal Y chromosomes. This band loses its fluorescence in some translocations, probably through a position effect. Hoechst 33258 staining does not produce any brightly fluorescing bands.