G-banding data are presented for a wide range of Australian marsupial species and one South American species, all of which have 2n= 14. The chromosome banding pattern in each of these species is very similar. Variations between species can be explained by structural changes internal to individual chromosomes. This evidence favors the hypothesis of a conserved complement common to both Australian and American marsupials and underlies the dominant role of chromosome fission in the evolution of this group.

The gekko Phyllodactylus marmoratus has at least three distinct chromosome races; 2n=39, 2n=26 ZZ/ZW and 2n=34. Specimens from these races are morphologically distinguishable, have a degree of habitat specialization and occur in a defined distribution. The 2n=36 race found in Eastern Australia is the presumed primordial type. The 2n=34 race occurs in Western Australia and is regarded as a fusion derivative. The 2n=36 ZZ/ZW race, which is only found on the Murray River system in Eastern Australia has a heteromorphic sex chromosome system present in the female. Giemsa banding suggests that this heteromorphism is the result of a pericentric inversion.

Marsupials occupy a phylogenetic middle ground that is very valuable in genome comparisons of mammal and other vertebrate species. For this reason, whole genome sequencing is being undertaken for two distantly related marsupial species, including the model kangaroo species Macropus eugenii (the tammar wallaby). As a first step towards the molecular characterization of the tammar genome, we present a detailed description of the tammar karyotype, report the development of a set of molecular anchor markers and summarize the comparative mapping data for this species.

Dot-like micro B chromosomes of Brachycome dichromosomatica were analysed for their sequence composition. Southern hybridization patterns of a total micro B probe to genomic DNA from plants with and without micro Bs demonstrated that the micro Bs shared sequences with the A chromosomes. In addition to telomere, rDNA and common A and B chromosome sequences, a new B-specific, highly methylated tandem repeat (Bdm29) was detected. After in situ hybridization with Bdm29 the entire micro B chromosome was labelled and clustering of the condensed micro Bs could be observed at interphase. A high number of Bdm29-like sequences were also found in the larger B chromosomes of B. dichromosomatica and in other Bs within the genus Brachycome.

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Dot-like micro B chromosomes of Brachycome dichromosomatica were analysed for their sequence composition. Southern hybridization patterns of a total micro B probe to genomic DNA from plants with and without micro Bs demonstrated that the micro Bs shared sequences with the A chromosomes. In addition to telomere, rDNA and common A and B chromosome sequences, a new B-specific, highly methylated tandem repeat (Bdm29) was detected. After in situ hybridization with Bdm29 the entire micro B chromosome was labelled and clustering of the condensed micro Bs could be observed at interphase. A high number of Bdm29-like sequences were also found in the larger B chromosomes of B. dichromosomatica and in other Bs within the genus Brachycome.

A translocation t(12;21)(q24.1;q21.5) is described in a woman with a history of recurrent spontaneous abortions. The break points of this translocation are compared with those of 30 other translocations described in the literature, and the following conclusions are drawn: 1) An excess of breaks occurs in the p arm of chromosome 12. 2) The distributions of breaks in the bands of chromosome 12 is significantly different from that expected on a random basis. 3) Translocations of chromosome 12 occur more often with chromosome 21 than any other chromosome, but these rearrangements do not involve a specific region of chromosome 12. 4) Most of the translocations were ascertained through their unbalanced meiotic products but seven translocations were "balanced". Of these "balanced" translocations, three individuals were abnormal and two were recurrent aborters. The concept that phenotypic outcome may be related to the gross structural characteristics of the translocation site is not supported in this study.