摘要:

The benzimidazole derivative Hoechst 33258 was added at various concentrations to human leukocyte cultures. After 16 or 24 h of treatment, with concentrations equal to or greater than 100 µg/ml of Hoechst 33258, a number of chromosomes showed regions in which the chromatin was undercontracted. The centromeric regions of chromosome 1 and, more rarely, of chromosomes 3 and 9 appeared to be decondensed. Short decondensed regions were also present on the long arms of chromosomes 1 and 2. The possible nature of these regions is discussed

ISSN:1424-8581    

DOI:10.1159/000130703

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

Cytogenetic evidence suggests that the caprids (sheep and goats) evolved from a common ancestor with a 2n=60 karyotype. Although goats (Capra) retained the primitive 2n=60 karyotype, sheep (Ovis) underwent a sequential reduction in the number of chromosomes by means of acrocentric translocation. The formation of the first metacentric autosome (Ml) occurred in the aoudad (Ammotragus) and urial (O. vignei), resulting in a 2n=58 karyotype. The G-bands are homologous, which implies both genotypes arose from a common ancestor, possibly a rupicaprid. Based on G-bands, acrocentric chromosomes 1 and 7 of the 2n=60 karyotype formed the Ml. The X chromosome, which is the second longest acrocentric in the 2n = 60 karyotype, became the longest acrocentric in Ammotragus and Ovis (2n = 58). The second pair of metacentrics to evolve, which is ranked in the M3 position of the 2n=54 karyotype, resulted from the translocations of acrocentric chromosomes 4 and 14 or 15 in the 2n = 60 karyotype. The M2 was the third pair of metacentrics to be formed and resulted from the translocations of acrocentric chromosomes 3 and 12 or 13 in the 2n = 60 karyotype. The G-bands of all 2n = 54 karyotypes are homologous, which indicates origin from a common ancestor. Evidence is presented that suggests a prezygotic selection is bringing about a reduction in diploid chromosome numbers. The possible roles of fission and fusion in the karyotypic evolution of Ovis are discussed.

ISSN:1424-8581    

DOI:10.1159/000130704

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

A linear relationship between the amount of rDNA present and the number of autoradiographic silver grains observed after rRNA-DNA hybridization in situ was demonstrated using male mouse meiotic tissue as a test system.

ISSN:1424-8581    

DOI:10.1159/000130705

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

A single triploid individual (3n = 75) of the California roach, Hesperoleucus symmetricus, was identified among a sample of nine specimens from the Russian River, California. The diploid number of H. symmetricus, as revealed by the karyotypes of the remaining eight specimens, is 50. Aside from the all-female triploid unisexual fishes, this is the first report of a triploid fish from the wild, and the second report of a triploid in a bisexual fish species. The most likely origin of the triploid was probably fusion of a haploid sperm with an unreduced ovum.

ISSN:1424-8581    

DOI:10.1159/000130706

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

Oocytes from CBA mice varying in age from 2 to 11 months were cultured to the metaphase II stage of meiosis and the chromosomes analyzed. The oocytes from three maternal age groups were compared with respect to the mean number of oocytes obtained per mouse, the frequency of maturation to metaphase II, and the frequency of numerical chromosome abnormalities. Both the mean number of oocytes obtained per mouse and the frequency of maturation decreased markedly with maternal age. The frequency of chromosome abnormalities in the oocytes increased with maternal age from the young to the middle-aged mice but dropped off in the oldest maternal age group. No hyperploid (n + 1) oocytes were observed in the young or old group of mice, but 5.2 % hyperploidy occurred in the middle-aged group. It is suggested that the lack of hyperploid oocytes in the old CBA females might be due to a threshold effect in which oocytes that are damaged by the number of univalents present at metaphase I become atretic and do not progress to metaphase II. The frequency of diploid (2n) oocytes was 1.7 % and was not maternal-age dependent.

ISSN:1424-8581    

DOI:10.1159/000130707

出版商:S. Karger AG    

年代:1976

数据来源: Karger

ISSN:1424-8581    

DOI:10.1159/000130708

出版商:S. Karger AG    

年代:1976

数据来源: Karger