Duplication of the autosomally inherited 6-phosphogluconate dehydrogenase gene locus in tetraploid species of cyprinid fish

In with the old, in with the new: the promiscuity of the duplication process engenders diverse pathways for novel gene creation

The gene duplication process has exhibited far greater promiscuity in the creation of paralogs with novel exon-intron structures than anticipated even by Ohno. In this paper I explore the history of the field, from the neo-Darwinian synthesis through Ohno's formulation of the canonical model for the evolution of gene duplicates and culminating in the present genomic era. I delineate the major tenets of Ohno's model and discuss its failure to encapsulate the full complexity of the duplication process as revealed in the era of genomics. I discuss the diverse classes of paralogs originating from both DNA- and RNA-mediated duplication events and their evolutionary potential for assuming radically altered functions, as well as the degree to which they can function unconstrained from the pressure of gene conversion. Lastly, I explore theoretical population-genetic considerations of how the effective population size (N(e)) of a species may influence the probability of emergence of genes with radically altered functions.

Isozyme expression in F1 hybrids between carp and goldfish

Interspecific genetic differences in malate dehydrogenase (MDH), lactate dehydrogenase (LDH), superoxide dismutase (SOD), and esterase (EST) isozymes in carp (Cyprinus carpio) and goldfish (Carassius auratus) were used to examine the allelic expressions in the hybrid between these species. A unique liver SOD and muscle LDH phenotype unambiguously identifies all presumed hybrid individuals. There was no evidence of F2 or backcross phenotypes in hybrid individuals. Liver MDH and EST phenotypes in hybrids show a preferential expression of goldfish isozymes. Variation in the levels of carp liver MDH isozymes may result from the polymorphism of a regulatory mutation effecting isozyme expression, leading to gene silencing after duplication.

Biochemical genetics of Fundulus heteroclitus (L.). III. Inheritance of isocitrate dehydrogenase (Idh-A and Idh-B), 6-phosphogluconate dehydrogenase (6-Pgdh-A), and serum esterase (Est-S) polymorphisms

Starch gel electrophoresis has shown that natural populations of Fundulus heteroclitus have variants at four enzyme-coding loci: Idh-A, Idh-B, 6-Pgdh-A, and Est-S. Analysis of the phenotypic distribution of the F1 generation suggests that each of the variants segregates as autosomally inherited codominant alleles. Tissue specificity and intracellular localization were also determined for the IDH and 6PGDH isozymes.

Duplicate gene expression in diploid and tetraploid loaches (Cypriniformes, Cobitidae)

Botia macracantha and B. modesta have been demonstrated to be tetraploid species on the basis of their karyotypes and on the basis of the expression of a number of isozymes encoded by duplicate loci. A rather low percentage of duplicate loci was detected by electrophoresis, compared to that for other tetraploid Cypriniformes. Several hypotheses have been advanced to account for the low levels of duplicate gene expression observed. Lastly, many of the duplicate loci have diverged to unique patterns of expressions in different tissues or different levels of activity within a single tissue.

GENETIC STRUCTURE OF HORDEUM JUBATUM. I. OUTCROSSING RATES AND HETEROZYGOSITY LEVELS

The inheritance patterns of four allozyme systems were studied in the tetraploid weed, Hordeum jubatum L. The allozymes are: two cathodal peroxidase systems, CPX-2 and CPX-6, one glutamate oxaloacetate transaminase system, GOT-2, and one esterase system, EST-4. Using these systems outcrossing rates in two populations were calculated to be 1 to 3%. Because of intensive inbreeding, there is little heterozygosity at any of the loci examined in three sample populations. In the GOT and EST systems, however, duplicated loci resulting from polyploidy produce high levels of fixed heterozygosity. In the EST system, both heterozygous and homozygous phenotypes can occur in high frequencies in a population. The underlying genotypic flexibility may be the result of duplicated loci segregating for the same alleles, or for null alleles. The combination of self-fertilization, polyploidy, and duplicated loci with genotypic flexibility may contribute to the successful weedy nature of H. jubatum.

A genetic model for the evolution of the glycosphingolipids

The glycosphingolipids have been found in many animal tissues, but the complexity of their molecular structure varies considerably among the different phyla. Relatively simple structures have been found in invertebrate species, while the most complex have been demonstrated in brain tissue of modern fishes and amphibians. The data on the phylogenetic distribution of the glycosphingolipids has been interpreted to indicate that a significant number of gene duplications, involving many different structural genes, may have occurred during a few specific periods of vertebrate evolution. The transition from invertebrate to jawless vertebrate, the divergence of rays and skates from true sharks, the advent of modern bony fishes and the transition from aquatic to terrestrial vertebrates, each could have veen accompained by duplications of genes involved in the synthesis and degradation of glycosphingolipids. The evolutionary study of such a multi-enzyme system may be one means to detect alterations in the genome as a whole. The apparent correspondence in time of these gene duplications involved in glycosphingolipid metabolism and periods of rapid vertebrate evolution which may have been accompanied by significant increases in the amount of cellular DNA suggests that such changes may have occurred via the mechanism of tetraploidization.