Polyploidy in vertebrate ancestry: Ohno and beyond

Over 30 years ago, Susumu Ohno proposed that two rounds of polyploidy occurred early in vertebrate evolution. We re-examine this proposal using three recent lines of evidence. First, total gene number estimates from completely sequenced genomes suggest an increase in total gene number somewhere along the vertebrate or prevertebrate lineage, compatible with Ohno's model. Second, analyses of homeobox and other genes from amphioxus reveal very extensive gene duplication specifically on the vertebrate lineage. This refines the timing of putative polyploidy to after the divergence of amphioxus and vertebrates. Third, the existence of four-fold paralogy regions in the human genome is suggestive of two rounds of polyploidy, although other explanations are possible. We propose an experimental test, based on chromosomal localization of genes in amphioxus, that should resolve whether paralogy regions are indeed remnants of duplication in vertebrate ancestry.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 425–430.     

Structural Differences in the Hinge Region of Human Gamma A Myeloma Proteins of Different Subclasses

THE two antigenic subclasses of human γA myeloma proteins that have been identified are γA₁ and γA₂ (refs. 1-3). H—H interchain disulphide bonds are present in molecules of both subclasses, but H—L interchain disulphide bonds are present only in γA₁ proteins and the minor allotype of γA₂, Am 2–(ref. 4). Light chains of Am 2+ γA proteins occur as disulphide bonded dimers non-covalently linked to the heavy chains⁵.     

The relationship between body size and population size in bromeliad tank faunas

Relationships between body size and abundance in collections of animals from the tanks of 73 bromeliads belonging to five species were analysed. Unlike data in previously published studies on this relationship, these collections of species are not taxonomically restricted and represent complete communities over the macroscopic range of organisms. There is no overall tendency for there to be a positive or negative relationship between population abundance and body size of morphospecies. We can find no evidence that body size-abundance patterns are triangular in complete communities. However, there is weak evidence that the relationship in the aquatic subsets of those communities may have some underlying triangularity, with medium-sized species having the largest populations.