The maize abnormal chromosome 10 (Ab10) haplotype encodes a meiotic drive system that converts heterochromatic knobs into centromere-like bodies that are preferentially segregated through female meiosis. Ab10 was first described in the 1940s and has been intensively studied. Here I provide a comprehensive review of the literature, starting from the discovery of knobs and Ab10, preceding through the classic literature, and finishing with molecular structure and mechanisms. The defining features of the Ab10 haplotype are its two specialized kinesins, Kinesin driver and TR-1 kinesin, that activate neocentromeres at knobs containing different classes of the tandem repeat. In most Ab10 haplotypes, the two kinesin/knob systems cooperate to promote maximum meiotic drive. However, recent interpretations suggest that each kinesin/knob system can function as an independent meiotic driver and that in some cases they compete with each other. Ab10 is present at low frequencies throughout the genus Zea and has significantly expanded genome size by promoting the formation of knobs throughout the genome.

Cytogenetics, which is considered a fundamental tool to understand basic genetic and genomic issues of species, has greatly contributed to the description of polymorphisms both at inter- and intra-specific level. In fact, cytogenetics was one of the first approaches used to propose Anastrepha fraterculus (Diptera: Tephritidae) as a complex of cryptic species. Different morphological variants of sex chromosomes have been reported among Argentinean populations of Anastrepha fraterculus. However, since this high structural variability in sex chromosomes does not pose a reproductive barrier, their role in speciation is yet to be unveiled. This review provides an update on general aspects of cytogenetics in Argentinean Anastrepha fraterculus populations, focused on the prevalence of X-Y arrangements.

Lizards of the family Teiidae (infraorder Scincomorpha) were formerly known as Macroteiidae. There are 13 species of such lizards in the Amazon, in the genera Ameiva (Meyer, 1795), Cnemidophorus (Wagler, 1830), Crocodilurus (Spix, 1825), Dracaena (Daudin, 1801), Kentropyx (Spix, 1825) and Tupinambis (Daudin, 1802). Cytogenetic studies of this group are restricted to karyotype macrostructure. Here we give a compilation of cytogenetic data of the family Teiidae, including classic and molecular cytogenetic analysis of Ameiva ameiva (Linnaeus, 1758), Cnemidophorus sp.1, Kentropyx calcarata (Spix, 1825), Kentropyx pelviceps (Cope, 1868) and Tupinambis teguixin (Linnaeus, 1758) collected in the state of Amazonas, Brazil. Ameiva ameiva, Kentropyx calcarata and Kentropyx pelviceps have 2n=50 chromosomes classified by a gradual series of acrocentric chromosomes. Cnemidophorus sp.1 has 2n=48 chromosomes with 2 biarmed chromosomes, 24 uniarmed chromosomes and 22 microchromosomes. Tupinambis teguixin has 2n=36 chromosomes, including 12 macrochromosomes and 24 microchromosomes. Constitutive heterochromatin was distributed in the centromeric and terminal regions in most chromosomes. The nucleolus organizer region was simple, varying in its position among the species, as evidenced both by AgNO3 impregnation and by hybridization with 18S rDNA probes. The data reveal a karyotype variation with respect to the diploid number, fundamental number and karyotype formula, which reinforces the importance of increasing chromosomal analyses in the Teiidae.

High mobility group (HMG) proteins are an abundant class of chromosomal proteins facilitate assembly of higher order structures. The mammalian HMG proteins have been grouped into three distinct families on the basis of their characteristic functional sequence: the HMGB, the HMGN, and the HMGA family. The HMG proteins of Drosophila melanogaster and Chironomus tentans are the best characterized dipteran insect HMG proteins. Three abundant members of this group of nonhistone proteins were detected in those insects. Two of them belong to the HMGB family and one to the HMGA family. The possible relatedness of these proteins to the formation of higher order nucleoprotein structures and their possible role in the regulation of transcription is discussed.

Telomeres are structurally and functionally complex. They consist of an array of simple DNA repeats at the extreme end of the chromosome with a more complex array of repeats adjacent to it. A large number of proteins have been identified that bind to the telomeric DNA repeats or to the protein complexes that are built at the chromosome end. Telomeres tend to form associations with each other. These associations have been implicated in the formation of nuclear domains that may be important for transcriptional regulation, for sister chromatid pairing at mitosis, and for homologous meiotic synapsis. Telomeric chromosome ends do not cause delays in cell cycle progression, nor are they subject to DNA repair as are broken chromosome ends. Telomeres also provide a separate mechanism for adding additional copies of the telomeric DNA to chromosome ends. This is needed to counterbalance the loss of DNA sequences from chromosome ends due to incomplete DNA replication. The components that participate in the latter mechanism and this process have been characterized in detail; the other functions of telomeres are less well understood but are the subjects of active investigation.

A revision of the standardized karyotype of deer mice (Peromyscus) is presented. This revision addresses short-comings of the original standardization, contains a substantial increase in the number of G-band markers and provides a nomenclature for the G-bands of each autosome and the X chromosome. Using the revised standardized karyotype, we specify the particular G-bands or patterns that identify each chromosome and catalog the more problematic chromosome identifications and likely misidentifications. For each chromosome, we present an overview of previously reported variation in euchromatic arrangement and heterochromatic constitution. We then review previous applications of the standardized karyotype and summarize the predominant findings from cytogenetic and cytosystematic studies of Peromyscus and related taxa.

Data over a 20-year period of investigation on C-polymorphism in parents of children with chromosome abnormalities, in couples with reproductive failures, and in patients with chromosome abnormalities are reviewed. The majority of the relevant evidence is suggestive of a relationship between C-polymorphisms and an enhanced risk of aneuploid progeny. It is suggested that phenomenon of \"interchromosomal effect\" of C-variants is accounted for by meiotic non-homologous co-orientation. Data on accumulation of marker variants in patients with chromosome abnormalities implicate the involvement of some prevalent segregation mechanism which is out of the limits of the models of meiosis considered.

A further patient with the ICF syndrome (immunodeficiency, centromeric heterochromatin instability of chromosomes 1, 9 and 16 and facial anomalies) is described. This case is the second to be reported with consanguinity of the parents. This lends support to the theory of autosomal recessive inheritance. The features of the 15 published cases are reviewed. The clinical and cytogenetic characteristics of the syndrome are discussed, and new evidence provided as to the role of centromeres and centric heterochromatin in the production of chromosome aberrations. Correspondence with other authors has made possible a review of the clinical outcome in this condition.

Two women with primary amenorrhoea and few other stigmata of Turner\'s syndrome were found to be chromosome mosaics: 45,X/46,X,idic(Y). In Case 1, the dicentric isochromosome Y was found to have a long-arm breakpoint of formation. This structure was interpreted as containing two Y short arms and centromeres separated by a region derived from the proximal Y long arm. One of the centromeres in the Case 1--idic(Y) was suppressed in 80% of cells in blood, and in these cells it appeared as a regular Y-shaped chromosome. In Case 2 the idic(Y) was derived by a short-arm breakpoint of formation. In all the dicentrics of this case with one primary constriction (functional monocentrics) there was a single Cd band. In the 10% of dicentrics with two primary constrictions, there were two Cd bands. It is argued that the instability of sex isochromosomes is due to this functional dicentricity in some cells. These cases are compared with 42 other Y isochromosomes with various short- and long-arm breakpoints of formation. It is suggested that some of the nonheterochromatic, nonfluorescent Y chromosomes previously reported may be explained as dicentric i(Y) with proximal long-arm breakpoints of formation and one suppressed centromere.