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Five families are traditionally recognized within higher ruminants (Pecora): Bovidae, Moschidae, Cervidae, Giraffidae and Antilocapridae. The phylogenetic relationships of Antilocapridae and Giraffidae within Pecora are, however, uncertain. While numerous fusions (mostly Robertsonian) have accumulated in the giraffe's karyotype (Giraffa camelopardalis, Giraffidae, 2n = 30), that of the pronghorn (Antilocapra americana, Antilocapridae, 2n = 58) is very similar to the hypothesised pecoran ancestral state (2n = 58). We examined the chromosomal rearrangements of two species, the giraffe and pronghorn, using a combination of fluorescence in situ hybridization painting probes and BAC clones derived from cattle (Bos taurus, Bovidae). Our data place Moschus (Moschidae) closer to Bovidae than Cervidae. Although the alternative (i.e., Moschidae + Cervidae as sister groups) could not be discounted in recent sequence-based analyses, cytogenetics bolsters conclusions that the former is more likely. Additionally, DNA sequences were isolated from the centromeric regions of both species and compared. Analysis of cenDNA show that unlike the pronghorn, the centromeres of the giraffe are probably organized in a more complex fashion comprising different repetitive sequences specific to single chromosomal pairs or groups of chromosomes. The distribution of nucleolar organiser region (NOR) sites, often an effective phylogenetic marker, were also examined in the two species. In the giraffe, the position of NORs seems to be autapomorphic since similar localizations have not been found in other species within Pecora.

Despite marked improvements in the interpretation of systematic relationships within Eutheria, particular nodes, including Paenungulata (Hyracoidea, Sirenia and Proboscidea), remain ambiguous. The combination of a rapid radiation, a deep divergence and an extensive morphological diversification has resulted in a limited phylogenetic signal confounding resolution within this clade both at the morphological and nucleotide levels. Cross-species chromosome painting was used to delineate regions of homology between Loxodonta africana (2 n =56), Procavia capensis (2 n =54), Trichechus manatus latirostris (2 n =48) and an outgroup taxon, the aardvark ( Orycteropus afer , 2 n =20). Changes specific to each lineage were identified and although the presence of a minimum of 11 synapomorphies confirmed the monophyly of Paenungulata, no change characterizing intrapaenungulate relationships was evident. The reconstruction of an ancestral paenungulate karyotype and the estimation of rates of chromosomal evolution indicate a reduced rate of genomic repatterning following the paenungulate radiation. In comparison to data available for other mammalian taxa, the paenungulate rate of chromosomal evolution is slow to moderate. As a consequence, the absence of a chromosomal character uniting two paenungulates (at the level of resolution characterized in this study) may be due to a reduced rate of chromosomal change relative to the length of time separating successive divergence events.

G- and C-banding delimits two cytogenetic groups within the vlei rat, Otomys irroratus. One has a diploid number of 2n = 24, resulting from a centric fusion of chromosomes 7 and 12 of the O. irroratus standard coupled with a tandem fusion to chromosome 8. The second has a diploid number of 2n = 28, lacks the compound chromosome, and appears to have a far wider geographic distribution within South Africa. Additionally, the two groups differ through the presence of cytotype-specific heterozygous centric fusions and one to three B chromosomes which appear as floating polymorphisms in the 2n = 28 complex.

Comparative cytogenetics and fluorescence in situ hybridization (FISH) were used to track structural rearrangements in the X chromosomes of two African antelope species, the eland (Taurotragus oryx; tribe Tragelaphini) and the suni (Neotragus moschatus; tribe Neotragini). Using two microdissected cattle chromosome painting probes (one specific for Xp-containing sequences corresponding to Xp24→p12 of the cattle X, and one specific for Xq-containing sequences corresponding to Xq12→qter), we show that intrachromosomal rearrangements distinguish the X chromosomes of these species. Furthermore, there is clear evidence that, superimposed on this background of intrachromosomal evolutionary change, the sequences contained in the cattle Xp painting probe appear to have moved as a complete unit during the repatteming of the bovid X. Although we are unable to infer the order of the rearranged chromosomal segments, given the large regions of homology detected by the chromosome paints, we nonetheless believe that this approach (combining conventional and molecular cytogenetic studies on the X chromosome) will prove useful for inferring phylogenetic relationships in the family Bovidae, particularly as more probes become available.

Geographic chromosomal variation, which in many instances does not correlate with variation in phenotype, is increasingly being detected within both large and small species of mammals. We argue that this cryptic chromosome variation can pose a significant threat to translocation practices involving the admixture of specimens between geographically distant populations. Matings between individuals characterized by different cytotypes can result in perinatal mortality or, at a later stage, in reduced fertility of offspring heterozygous for chromosomal rearrangements. This can thus impact heavily on the species, or population, that management is trying to conserve. Some of the more frequently encountered structural rearrangements in mammals and the possible deleterious effects that these can have in the heterozygous condition are reviewed and guidelines proposed for the use of cytogenetics as a conservation tool in wildlife management.

Cytogenetic analysis yields important objective information that has been shown to correlate with both patient response to therapeutic intervention and patient survival. Bone marrow samples are submitted to a common reference laboratory for cytogenetic analysis from children with newly diagnosed acute lymphoblastic leukemia (ALL) registered on frontline Pediatric Oncology Group (POG) therapeutic studies (classification 8600 series). A portion of the sample from the Texas Children's Hospital (Houston, TX) a POG affiliate, was also submitted to a local cytogenetics laboratory for analysis. This study retrospectively compares karyotypic data and methods from the Laboratory of Medical Genetics, University of Alabama at Birmingham (reference laboratory) with those of the Kleberg Cytogenetics Laboratory at the Baylor College of Medicine (local laboratory) over a 35-month period to evaluate the effect of differences in specimen procurement, handling, and laboratory methodology on yield of cytogenetic information. Each laboratory was able to identify clonal abnormalities in 72% of cases examined during the last year of the study. When these data were combined, the overall detection rate of clonal abnormalities was 87.5%. Utilizing the same bone marrow aspirate from 73 children, this study demonstrates that cytogenetic methodology significantly affects the yield of identifiable clonal abnormalities, while variables such as overnight shipping have no discernable effect. This study also supports the contention that central laboratory testing effectively yields information critical to ongoing large-scale research endeavors.

Fetal blood sampling has been used in the genetic work-up of twin gestations for rapid karyotyping. We present a case of twins which on ultrasound evaluation revealed hydrops fetalis in one twin and a normal second twin. Fetal blood sampling revealed the presence of mosaicism for 46,XY/45,X in both twins. HLA antigen testing showed the twins to be identical. The patient elected pregnancy termination. Blood chromosomal analysis after delivery revealed both twins to have 46,XY/45,X mosaicism, but the twin with signs of hydrops fetalis had tissue chromosomes of 45,X and the normal twin had tissue chromosomes of 46,XY. Amniotic fluid chromosomal analysis revealed 46,XY in twin A and 45,X in twin B. This represents a case of identical (monozygotic) twins with sex discordance. In this case, there was the probable occurrence of post-zygotic chromosomal non-disjunction leading to the discordancy of the sex in this set of twins. With the presence of vascular communication in monozygotic twins, there is the possibility of exchange of blood in monozygotic twins and the result of blood chimerism in twins.

Leber congenital amaurosis (LCA, MIM 204000) accounts for at least 5% of all inherited retinal disease1 and is the most severe inherited retinopathy with the earliest age of onset2. Individuals affected with LCA are diagnosed at birth or in the first few months of life with severely impaired vision or blindness, nystagmus and an abnormal or flat electroretinogram (ERG). Mutations in GUCY2D (ref. 3), RPE65 (ref. 4) and CRX (ref. 5) are known to cause LCA, but one study identified disease-causing GUCY2D mutations in only 8 of 15 families whose LCA locus maps to 17p13.1 (ref. 3), suggesting another LCA locus might be located on 17p13.1. Confirming this prediction, the LCA in one Pakistani family mapped to 17p13.1, between D17S849 and D17S960—a region that excludes GUCY2D. The LCA in this family has been designated LCA4 (ref. 6). We describe here a new photoreceptor/pineal-expressed gene, AIPL1 (encoding arylhydrocarbon interacting protein-like 1), that maps within the LCA4 candidate region and whose protein contains three tetratricopeptide (TPR) motifs, consistent with nuclear transport or chaperone activity. A homozygous nonsense mutation at codon 278 is present in all affected members of the original LCA4 family. AIPL1 mutations may cause approximately 20% of recessive LCA, as disease-causing mutations were identified in 3 of 14 LCA families not tested previously for linkage.

G-banded and C-banded karyotypes of three closely related and morphologically similar species of cotton rats, Sigmodon hispidus (2n = 52; 52 autosomal arms), S. mascotensis (2n = 28; 28 autosomal arms), and S. arizonae (2n = 22,24; 38 autosomal arms) are presented and compared. Despite the enormous difference between the higher diploid number of hispidus and the lower diploid numbers of mascotensis and arizonae, a great deal of G-band homology is retained. If the karyotype of hispidus is considered ancestral in the group, then chromosome evolution toward lower diploid numbers has proceeded through the fixation of a large number of both tandem and centric fusions. Centromeric heterochro-matin has not, however, persisted as interstitial C-band material on the tandem fusion products. The karyotypes of mascotensis and arizonae share several tandem fusion products of hispidus chromosomes indicating a common origin of the former two species from an ancestor of intermediate diploid number. Chromosome evolution from the ancestral hispidus-like karyotype to the karyotype of the common ancestor of arizonae and mascotensis proceeded almost exclusively by tandem fusion. This orthokaryotypic trend continued in the evolution of the karyotype of modern mascotensis. In the line leading from the arizonae-mascotensis ancestor to modern arizonae a trend of centric fusion predominated.

The banding patterns of mitotic chromosome from three cottontail species, Sylvilagus aquaticus (2n = 38), S. floridanus (2n = 42), and S. transitionalis (2n = 46), are presented and compared with those of the proposed leporid ancestral karyotype, the latter being reflected in a species of hare, Lepus saxatilis (2n = 48). The differences in the diploid numbers of the cottontail species are primarily due to the fixation of Robertsonian fusions which have occurred during the evolution of their respective genomes. Of the eight fusion products identified, seven were species specific, while one, which is thought to reflect their more recent common ancestory, is shared by both S. aquaticus and S. floridanus. Other karyotypic differences include interspecific variation in the amount and distribution of constitutive heterochromatin, as well as the presence of two autosomal pairs in S. transitionalis which do not have apparent banding homologies either with the chromosomes of other cottontails or with those of the Lepus genome. The tendency for certain chromosomes in the ancestral karyotype to show a predisposition to undergo fusion events within the Leporidae is discussed.

Epididymal spermatozoa from 12 species of mammals were stained using silver nitrate and examined with the light microscope. Silver nitrate differentiates many of the gross morphological features of spermatozoa, including the acrosome, subacrosomal region, perforatorium, postacrosomal sheath, neck, dense outer fibers of the core of the midpiece, annulus, principal piece, and end piece. Silver-staining patterns of spermatozoa reveal both species-specific and strain-specific differences, particularly of the sperm head. The biochemical basis of silver staining may be due in part to the presence of sulfhydryl- and disulfide-rich proteins; however, it cannot be explained entirely by the presence of these moieties. The detail obtained using silver nitrate staining, coupled with the ease and rapidity of the procedure, should be useful to workers in many areas of biological and medical research.

We have used aqueous silver nitrate to stain preparations of formalin-fixed meiotic cells. In doing so we have “rediscovered” a number of spermatid organelles, such as nuclear rings, acrosomal cap rings, centriolar adjuncts, and developing annuli, apparently not seen in numerous other recent studies of silver-stained meiotic cells. The availability of these structures for light microscopy coupled with the ease of preparation of the samples should facilitate studies on spermatid development, cytochemistry, and differentiation.

In situ hybridization of radiolabeled fibrinogen cDNAs to human and rat metaphase chromosomes has shown that the genes encoding the Aα, Bβ, and γ fibrinogen subunits are syntenic in both species. Our data localize the human fibrinogen gene cluster to band q31 on chromosome 4, thereby confirming and extending previous map assignments of these genes in man. We have also assigned these genes to the q31→q34 region of rat chromosome 2. This is the first map assignment of these genes in the rat and also the first report to clearly establish linkage of the Bβ subunit gene to the Aα and γ genes in this species.

We report a case of acute nonlymphoblastic leukemia (M5) with a rare cytogenetic abnormality involving chromosomes 8 and 16, t(8;16)(p11;p13). The leukemic blasts were determined to be monocytic by cytochemical and immunochemical studies. Morphological changes of the leukemic cells in response to phorbol myristate acetate further supported their identification as monocytic in nature. This chromosomal abnormality has apparently been reported only thrice in the literature. Translocation (8;16)(p11;p13), though rare, may be of primary importance in the process of leukemogenesis in some cases of histiocytic/monocytic malignancies.

Chromosomes from cultured fibroblasts of four cottontail species (Sylvilagus audubonii, 2n = 42; S. idahoensis, 2n = 44; S. nuttallii, 2n = 42; and S. palustris, 2n = 38) were analyzed using G- and C-banding techniques. The evolutionary restructuring of the genomes of these species was traced by comparing their banded chromosomes to those of Lepus saxatilis, a species of hare in which the leporid ancestral karyotype is thought to have been conserved. Chromosomal evolution appears to have proceeded primarily through changes in the amount and distribution of heterochromatin and through fixation of Robertsonian fusions. Excluding heterochromatic differences, S. audubonii and S. nuttallii are karyotypically very similar, as are S. aquaticus and S. palustris (previously reported). The genome of the taxonomically controversial species S. idahoensis, compared to other cottontail species, is markedly impoverished in C-band material. These data and those of cottontail species previously described in the literature are incorporated in two alternative phylogenetic schemes.

Silver-stained pachytene cells of male cotton rats, Sigmodon julviventer, heterozygous for a naturally occurring Robertsonian fusion, were examined by light microscopy. Silver staining clearly revealed synaptonemal complexes of all autosomal bivalents and of the translocation trivalent, as well as X-Y conformations within the sex vesicle. The synaptonemal complex of the trivalent conforms closely in morphology to that observed by electron microscopy in hybrids of other species. In all cases, the proximal telomeric knobs of the two acrocentric elements were paired and projected in the same direction from the metacentric element. The geometry of trivalent pairing in pachytene may predispose to normal disjunction and, therefore, account for the high fertility observed in 5. julviventer heterozygotes.

We report a simple, dependable method for stimulating bone marrow mitosis in small mammals. Subcutaneous injections of a suspension of active baker’s yeast may elevate the mitotic index as much as six times or more. Additionally, the metaphases obtained are easily spread when air dried, and the chromosomes are readily banded. This method should prove useful to investigators who wish to use bone marrow as a source of chromosomes for cytotaxonomic studies or for studies of specific chromosome damage in vivo.

The meiotic behavior of silver-stained X and Y chromosomes of the Virginia opossum, Didelphis virginiana, and the southern pygmy mouse, Baiomys musculus, was studied by light microscopy. While the sex chromosomes of these two species differ in both size and morphology, their meiotic behavior is very similar. In both species, a typical sex vesicle is formed during pachytene, but unlike most other mammalian species thus far studied, a synaptonemal complex does not form between the X and Y chromosomes. During pachytene, variable modes of association of the ends of the sex chromosomes (both heterologous and autologous) are sometimes observed. During diplotene, diakinesis, and metaphase I, the X and Y rarely appear to be associated. In some pachytene nuclei of B. musculus, the single axis of the biarmed X chromosome folds back upon itself, and the telomeres form a close association. While synaptic pairing segments of the sex chromosomes of the Virginia opossum may be displaced by telomeric heterochromatin on the X, true pairing regions between the X and Y of the pygmy mouse may be lacking.

Splenic lymphocytes from Sprague Dawley and Fischer 344 rats were exposed to two chemicals known to induce common fragile site expression in man: fluorodeoxyuridine (in conjunction with the enhancing effects of caffeine) and aphidicolin. Of 39 sites that were significantly damaged in excess, 12 meet the criteria for fragility proposed in this investigation. Rat fragile sites appear to differ from those in man in that no common hierarchical frequency of expression is evident from the two methods of induction. In addition, a comparison of published cancer-specific chromosome breakpoints from a variety of rat tumors reveals little or no apparent concordance with the identified fragile sites. The rat is an animal model in which multiple common fragile sites can be induced and, as such, will be valuable for testing hypotheses concerning the biological basis of chromosomal fragility.

Nineteen fragile sites induced by aphidicolin in lymphocyte cultures from the laboratory mouse are documented. These sites are compared with previously described fragile sites induced in mouse fibroblast systems, and then with those reported on chromosomes which have been evolutionarily conserved between the mouse and the laboratory rat. Of a total of 38 fragile sites thus far identified in mouse fibroblasts and lymphocytes, only 4 sites are common to the two cell types; 34 sites show no correspondence of loci. The reason for this discrepancy is unclear, but it is possible that these data may indicate some degree of tissue specificity of fragile site expression in the mouse. Eight autosomes in the mouse and rat retain straightforward and nearly complete banding homology. To test the hypothesis that fragile sites are conserved between the two species, we compared these eight autosomes with regard to number and distribution of fragile site loci. A total of 30 fragile sites is distributed over the conserved chromosomes. Only 4 (possibly 5) are common to both species; 18 are found in the rat but not the mouse, and 4 are found in the mouse but not the rat. Of the 4 shared sites, notable differences in frequency of expression exist. Our comparisons show that: (1) a small number of fragile sites is conserved; (2) a large number of fragile sites is not conserved, and (3) some sites which are conserved are quite different in the frequency at which they are expressed in the two species, indicating that the sites themselves may have undergone evolutionary change.(ABSTRACT TRUNCATED AT 250 WORDS)

The G- and C-banded chromosomes of six species of hare (genus Lepus) are presented and compared. No variation in gross chromosome morphology or banding pattern was observed indicating that speciation in this widespread genus has not involved karyotypic change.

Chromosomal homologies among the X chromosomes of species representative of eight bovid subfamilies and most of the recognized tribes were established using a combination of FISH and conventional G- and C-banding. Our analyses allowed for the delimitation of three X chromosome types represented, respectively, by cattle (Bovinae, tribe Bovini), the tragelaphines (Bovinae, tribe Tragelaphini), and a large assemblage comprising all the remaining subfamilies and their tribes (the Cephalophinae, Hippotraginae, Alcelaphinae, Antilopinae, Aepycerotinae, Peleinae, and Caprinae). The use of the bacterial artificial chromosome probe BAC 101 (which maps to Xp12 in cattle) and an Xp painting probe comprising sequences specific for the short arm of cattle Xp (Xp24→p12) allowed us to orient this region, which has moved as a conserved euchromatic block during the evolution of the bovid X chromosome. We show that the differences between the three chromosomal types are attributable to a transposition, two inversions, and heterochromatic additions/deletions. A paucity of comparative mapping data precludes the assignment of the sequences contained in cattle Xp to either the presumed conserved (XCR) or the recently added (XAR) region of the eutherian X chromosome, and the reasons for the retention of these sequences as an evolutionarily conserved unit in the intrachromosomal restructuring of the bovid X across lineages remain enigmatic.