Three subfamilies of genes are acknowledged within the zona pellucida (ZP) gene family. At present, these subfamilies each have two names that are used interchangeably: ZPA or ZP2, ZPB or ZP1, and ZPC or ZP3. The ZPA genes encode the longest protein sequences and the ZPC genes the shortest. Recently, several sequences, which have no clear relationship to the three subfamilies, have been identified. These sequences include two paralogous ZP genes from Xenopus laevis and a single gene from the fish Oryzias latipes. We have conducted extensive phylogenetic analyses of the known ZP genes. As well as establishing the evolutionary relationships among these genes, the analyses make it clear that the dual nomenclature system is no longer feasible, because major paralogous groups are present in the ZPB (ZP1) family of genes of amniotes. We propose a unified system of nomenclature for the ZP gene family that removes the existing ambiguities.

Mammals possess multiple, closely linked ␤-globin genes that differ in the timing of their expression during development. These genes have been thought to be derived from a single ancestral gene, by duplication events that occurred after the separation of the mammals and birds. We report the isolation and characterization of an atypical ␤-like globin gene (-globin) in marsupials that appears to be more closely related to avian ␤-globin genes than to other mammalian ␤-globin genes, including those previously identified in marsupials. Phylogenetic analyses indicate that -globin evolved from an ancient gene duplication event that occurred before the divergence of mammals and birds. Furthermore, we show that -globin is unlinked to the previously characterized ␤-globin gene cluster of marsupials, making this the first report of an orphaned ␤-like globin gene expressed in a vertebrate. The globin genes and their homologues have been studied in a wide range of species including bacteria, plants, and animals; as a consequence there exists a wealth of information on the structure, expression, and function of these genes (1). The availability of such an extensive data set, particularly that involving DNA sequences, has enabled the evolutionary history of the globin genes to be reconstructed to a level of detail that is probably unsurpassed by any other gene family.As originally postulated by Ingram (2) on the basis of partial amino acid sequences from several globin chains, it is now clear that primordial globin genes underwent a series of gene duplication events that led, in vertebrates at least, to a number of coordinately expressed genes that make up the present myoglobin, ␣-globin, and ␤-globin gene families (1). These duplication events have enabled specialized forms of globin to evolve that are physiologically adapted to the oxygen transport requirements in different tissues, at different developmental stages.We have been interested in exploiting the ancient evolutionary separation between monotremes, marsupials, and eutherian mammals (3) to determine the timing and nature of gene duplications that occurred in the ␤-globin gene family. It has become clear from our previous work on the dunnart (Sminthopsis crassicaudata; refs. 4-6), and from that reported by Koop and Goodman on the North American opossum (Didelphis virginiana; ref. 7), that the first duplication event that gave rise to the early-and late-expressed globin genes in mammals (as typified by the embryonically expressed -globin genes and the lateexpressed ␤-globin genes) occurred before the separation of marsupials and eutherians, approximately 120 million years ago. In contrast to the eutherian mammals that have a complex ␤-globin locus consisting, in humans for example, of five expressed genes and a pseudogene, marsupials, as exemplified by the dunnart and opossum, appeared to have a relatively simple ␤-globin gene cluster consisting of only two genes: -globin, expressed in embryos and newborn pouch young, and ␤-globin, expressed soon after birth and int...

The structure, function, and evolutionary history of globin genes have been the subject of extensive investigation over a period of more than 40 years, yet new globin genes with highly specialized functions are still being discovered and much remains uncertain about their evolutionary history. Here we investigate the molecular evolution of the beta-globin gene family in a marsupial species, the tammar wallaby, Macropus eugenii. We report the complete DNA sequences of two beta-like globin genes and show by phylogenetic analyses that one of these genes is orthologous to embryonically expressed epsilon-globin genes of marsupials and eutherians and the other is orthologous to adult expressed beta-globin genes of marsupials and eutherians. We show that the tammar wallaby contains a third functional beta-like globin gene, omega-globin, which forms part of the alpha-globin gene cluster. The position of omega-globin on the 3' side of the alpha-globin cluster and its ancient phylogenetic history fit the criteria, originally proposed by Jeffreys et al. (1980), of a "fossil" beta-globin gene and suggest that an ancient chromosome or genome duplication preceded the evolution of unlinked clusters of alpha- and beta-globin genes in mammals and avians. In eutherian mammals, such as humans and mice, omega-globin has been silenced or translocated away from the alpha-globin locus, while in marsupials omega-globin is coordinately expressed with the adult alpha-globin gene just prior to birth to produce a functional hemoglobin (alpha2 omega2).

The aim of this survey was to measure levels of genetic variation within and between 5 different strains of outbred Swiss mice. Ten to 15 animals from each strain (NIH, Q(S), ARC, IMVS and STUD) were typed, using allozyme electrophoresis, at 10 gene loci: Mod-1, Idh-1, Gpi-I, Es-1, Es-3, Hbb, Pep-3, Gr-1, Got-2 and Pgm-1. Polymorphic variation in at least one of the 5 strains was detected at all 10 loci. The proportion of polymorphic loci ranged from 0.3 (NIH) to 0.8 (IMVS) with a mean of 0.52. Average expected heterozygosities ranged from 0.08 (NIH) to 0.37 (IMVS) with a mean of 0.21. The inbred strain SWR was, as expected, homozygous at all 10 loci. The amount of allelic substitution between pairs of strains was quantified using Nei's genetic distance, and a dendrogram based on these genetic distances showed a close overall similarity in its branching pattern to the known genealogy of the strains. This survey showed that a considerable degree of genetic variation persists in the 5 strains examined, a level of variation similar to that previously detected by Rice and O'Brien (1980) in 3 other outbred Swiss strains.