摘要:

The sex chromosomes of the partly sympatric species of gerbils Gerbillus pyramidum and G. gerbillus (Mammalia: Gerbillinae) were investigated by a variety of light- and electron-microscope methods, including DNA replication banding and synaptonemal complex (SC) techniques. The sex-chromosome mechanism of G. pyramidum is of the JXY : XX type, whereas that of G. gerbillus is of the less common (JXYJY2 : XX system. The results include the demonstration that the X chromosomes of both species are compound. One segment is added to the X chromosome of G. pyramidum, leading to an increase in length from the standard 5% to approximately 7.3%, whereas two different extra segments increase the length of the X chromosome of G. gerbillus to approximately 11 % of the length of the haploid genome. In both cases the extra material is autosomal and is also represented in the respective Y chromosomes. Classifying heterochromatin by the variation in staining quality was helpful in elucidating the possible origin of the different chromosome segments, including the pericentromeric regions. Observations on meiotic chromosome pairing and chiasma formation have confirmed the homologies established by band comparisons. The occurrence of chiasmata between the sex chromosomes supports the autosomal origin of the pairing segments. These and other findings have been interpreted in the framework of a multistep evolutionary model. This sequence starts from a hypothetical pair of sex chromosomes, the X element of which amounts to 5% of the haploid genome, and leads through three translocations involving two pairs of autosomes and one pericentric inversion to the most complex situation of this series, manifested in G. gerbillus. The adaptive value, if any, of autosome incorporation into the sex chromosomes repeatedly occurring here is unknown. It is, however, a remarkable fact that in one species, G. gerbillus, the complex sex-chromosome constitution is conserved over vast geographic distances, and in the other, G. pyramidum, the compound X and Y chromosomes withstand change in the face of extreme autosome restructuring.

ISSN:1424-8581    

DOI:10.1159/000131863

出版商:S. Karger AG    

年代:1983

数据来源: Karger

摘要:

Karyotypes of the human C32r16 line and its HPRT” mutant derivatives were compared. All three HPRT- mutant strains (TG-A, TG-E1, and TG-E2) studied were hypotetraploid and arose by genomic duplication. TG-A and TG-E had distinct karyotypes, reflecting their independent clonal origins. Both TG-E1 and TG-E2 were similar karyotypically, except that TG-E2 differed from TG-E1 by the presence of two new sets of balanced translocations and a significantly higher number of new markers, viz., 24 new markers in 14 TG-E2 cells as compared to 2 new markers in 13 TG-E1 cells. Comparison of the hypothetical 2s karyotype of C32r16 with the modal karyotypes of the mutants revealed (1) that chromosome changes occurred more frequently among marker chromosomes (57.1%) than among normal chromosomes (18.1%) and also more frequently among tetrasomic (28.6%) than among disomic (3.3%) normal chromosomes, and (2) that one member of a group of paired marker chromosomes tended to be eliminated very frequently, whereas disomic normal chromosomes retained their disomic condition. Chromosome 7 was involved in the formation of new marker chromosomes twice as much as any other chromosome, and even increased to pentasomy in TG-E1. Chromosome changes associated with 6-thioguanine treatment are briefly discusse

ISSN:1424-8581    

DOI:10.1159/000131864

出版商:S. Karger AG    

年代:1983

数据来源: Karger

摘要:

A karyotypic comparison between the blue fox and the silver fox revealed conservation of the chromosome arm as a unit, except for large heterochromatic blocks in 10 pairs of blue fox chromosomes and the complete absence of a common metacentric autosomal pair. This finding seems to indicate that their karyotypes evolved from a common ancestral karyotype, characterized by 70–76 acrocentric autosomes, mainly through a series of independent centric fusion

ISSN:1424-8581    

DOI:10.1159/000131865

出版商:S. Karger AG    

年代:1983

数据来源: Karger

摘要:

The heterochromatin of the Chinese hamster sex chromosomes was analyzed by different banding techniques. Combined results obtained after differential Ba(OH)2 treatment, BrdU incorporation, Giemsa 11, and staining with quinacrine permitted the characterization of different regions in the heterochromatic portions of the X and Y chromosomes. In the light of these observations, the chiasma observed in the sex bivalent of Chinese hamster spermatocytes was localized within specific heterochromatic regions. The homologous segments consist of the entire short arm of the Y and the distal end of the long arm of the X up to band q21. These regions are probably not rich in highly repetitive DNA sequences, which are more resistant to alkali denaturation, or in satellite DNA, which is stained by Giemsa 11. Thus the heterochromatin in the homologous regions of the sex chromosomes allows the formation of a chiasma. The heterogeneity found in these heterochromatic regions may help to establish a more precise relationship between heterochromatin and recombination.

ISSN:1424-8581    

DOI:10.1159/000131866

出版商:S. Karger AG    

年代:1983

数据来源: Karger

摘要:

The karyotypes of six species of Carnivora (Mungos mungo, Paradoxurus hermaphroditus, Potos flavus, Mustelafuro, Felis serval, and Halichoerus grypus), representative of five different families, were studied and compared. Correspondence between almost all chromosome segments was found, and a presumed ancestral karyotype of Carnivora is proposed. Analogies to human chromosomes are also given, and the results obtained are in excellent agreement with previously published gene mapping data on man and the domestic cat.

ISSN:1424-8581    

DOI:10.1159/000131867

出版商:S. Karger AG    

年代:1983

数据来源: Karger

摘要:

Genetic analysis of the high frequency of X-Y chromosome dissociation found in primary spermatocytes of F1hybrids between Japanese wild mice (Mus musculus molossinus) and inbred laboratory mice (BALB/c) was attempted. The frequency of X-Y dissociation (X//Y) in both BALB/c and M. m. molossinus was lower than 30% (Low X//Y), while the value was more than 70% (High X//Y) in their F1 hybrids. Two types of progeny (High X//Y and Low X//Y) appeared in the backcross between BALB/c and High X//Y males, although the frequency of Low X//Y progeny decreased with increasing numbers of backcross generations (26.5% at N2, 13.2% at N3, 5.3% at N4, and 0% at N5). Low X//Y sires produced only Low X//Y mice. We hypothesize that at least one heritable factor which is responsible for the end-to-end association of the sex chromosomes (temporally symbolized as Sxa) is located on the common part of the X and Y crhomosomes. The Sxa allele of BALB/c is Sxaaand that of M. m. molossinus is Sxab. The genotype expected in High X//Y males is SxaajSxaband in Low X//Y males and their parental stocks either Sxaa/Sxaaor Sxab/Sxab. The repeated segregation of Low X//Y progeny from High X//Y sires is interpreted simply by assuming that crossing-over has occurred between the X and Y chromosomes. The gradual decrease in the recombinant type mice (Low X//Y) during sequential backcrosses suggests the presence of some autosomal factors that suppress the crossing-over of the sex chromosomes and that do not seem to function in the inter-subspecies hybrids.

ISSN:1424-8581    

DOI:10.1159/000131868

出版商:S. Karger AG    

年代:1983

数据来源: Karger

摘要:

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.

ISSN:1424-8581    

DOI:10.1159/000131869

出版商:S. Karger AG    

年代:1983

数据来源: Karger

摘要:

The expression of the fragile site on the X chromosome was examined in euploid somatic cell hybrids to determine if a normal genome could complement the abnormal genome and suppress fragile X expression. Fibroblasts from the patient showed the fragile X in 8% to 12% of cells, and fibroblasts from the normal individual showed no fragile X expression. Six fibroblast clones from the patient showed a variable frequency of fragile X expression (from 6.6% to 12%), suggesting that the fragile X is not expressed in a clonal fashion. Three clones from the normal individual did not show the fragile X. Four hybrid clones showed the fragile X in 5.6%, 4.0%, 7.0%, and 4.0% of cells, respectively, indicating that fragile X expression is not completely suppressed by the normal genome.

ISSN:1424-8581    

DOI:10.1159/000131870

出版商:S. Karger AG    

年代:1983

数据来源: Karger

摘要:

Iodinated cell surface polypeptides of human-mouse somatic cell hybrids were analyzed by one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis and high resolution two-dimensional gel electrophoresis in an effort to identify human gene products. Expression of two cell surface polypeptides was positively correlated with retention of specific human chromosomes: a polypeptide of molecular weight 250,000 and isoelectric point 8.3 with the human 5, and a polypeptide of molecular weight 250,000 and isoelectric point 7.0 with the human 2.

ISSN:1424-8581    

DOI:10.1159/000131871

出版商:S. Karger AG    

年代:1983

数据来源: Karger