摘要:

The karyo types of five turtles of the genus Podocnemis from the Amazon Region of Brazil were determined. Four species, P. cayennensis, P. expansa, P. sextuberculata and P. unifilis have 28 (2n) chromosomes and one, P. dumeriliana, has 26 (2n). No morphologically distinguishable sex chromosomes could be observed. The difference in number in P. dumeriliana can be explained by the occurrence of a centric fusion. The chromosome numbers in this genus are extremely low when compared with the range previously found in Chelonia (2n = 50 to 64).

ISSN:1424-8581    

DOI:10.1159/000130051

出版商:S. Karger AG    

年代:1969

数据来源: Karger

摘要:

In a human mosaic fibroblast culture consisting of a diploid cell line, 46, XY, t(Cp+;Dq–), and a trisomic cell line, 47, XY, D+, t(Cp+;Dq–), the frequency of trisomic cells initially decreased from 74% to 48% and then increased steadily through successive passages, until finally all diploid cells disappeared. The gradual predominance of trisomic cells coincided with the degenerative phase of the culture. It is speculated that although the genetically balanced diploid cells competed well in the beginning, they started their senescence earlier, thus giving way to the genetically unbalanced trisomic cells. Perhaps the same selective advantage of aneuploid cells over diploid cells could be shown in other mosaic cell cultures if they are maintained for longer peri

ISSN:1424-8581    

DOI:10.1159/000130052

出版商:S. Karger AG    

年代:1969

数据来源: Karger

摘要:

A proband girl was investigated because of a congenital heart defect and hexadactyly. Her brother and sister died in early infancy from cardiac malformations. In the patient, satellites were found on a chromosome No. 17 in 34% of cultured lymphocytes. The same cytological anomaly was discovered in the karyotype of her normal father. In addition, this man possessed a Y chromosome with satellites at the end of the long arm. The same satellited Y was demonstrated in the paternal grandfather and the abnormal No. 17 in the paternal grandmother. The satellited Y chromosome was found associated with group D and G chromosomes in over 30% of the metaphases in both men, strongly indicating a true nucleolar-organizing region and, therefore, a translocation from an autosome. Only a few associations were noted for the abnormal No. 17, where the appearance of satellites is probably due to a secondary constriction of a different nature. The identification of the two abnormal chromosomes was confirmed by autoradiography. A direct pathogenic significance of these structural anomalies is questionable.

ISSN:1424-8581    

DOI:10.1159/000130053

出版商:S. Karger AG    

年代:1969

数据来源: Karger

摘要:

Secondary chromosomal constrictions are thought to be the loci of the genome which code for ribosomal RNA synthesis. Their metaphase length could depend on nucleolar size or level of functional activity in interphase or on gene content. Wild-type frogs and a frog heterozygous for the Oxford nucleolar mutation were studied to determine which possibility is more probable. The mutant was studied because its single nucleolus is larger than wild-type nucleoli, it has only one constriction, half as many ribosomal genes, but produces the same amount of ribosomal RNA. The results indicate (1) that constriction length depends on the amount of genome (whereas others have shown nucleolar size to be related to level of activity) and (2) that the deletion is limited to the constricted segment, supporting the view that the constriction is the nucleolar organizer. Also, metaphase constrictions are longer than expected from their DNA content.

ISSN:1424-8581    

DOI:10.1159/000130054

出版商:S. Karger AG    

年代:1969

数据来源: Karger

摘要:

In this study we have used a method enabling associations between acrocentrics to be determined without recourse to any subjective measurements. By this method, with computer assistance, we were able to investigate the number and probability of occurrence of different types of acrocentric associations (D-D, G-G, D-G) in human male and female spread metaphases. The number of associations per cell are, in ascending order: G-G = 0.28; D-D = 0.37; D-G = 0.91. Their probability of occurrence per 100 cells is, in ascending order: D-D = 2.45; D-G = 3.82; G-G = 4.64. The results show that, on a per cell basis, the most numerous associations are between D and G chromosomes (D-G) because of the greater number of combinations possible. But in terms of chromosome pairwise associations, the clearest probability, or trend, to association seems to be within group G (G-G).

ISSN:1424-8581    

DOI:10.1159/000130055

出版商:S. Karger AG    

年代:1969

数据来源: Karger

摘要:

The hindquarters of two batches each of five young adult male mice were exposed to an acute dose of 1,200 R of 250-kV X-rays in two fractions of 600 R, separated by a period of eight weeks. Means of 41.2% and 32.6% spermatocytes with one or more multivalent configuration were found when the mice were killed 13 to 18 and 59 weeks, respectively, after the second dose. The multivalent configurations were attributed to reciprocal transloeations induced in spermatogonia. Other types of chromosomal abnormality were rare. 150 sons were tested for semi-sterility and subsequently examined cytologically. Five were found to be translocation heterozygotes. One other was cytologically normal but nevertheless exhibited semi-sterility and transmitted this character to some of its descendents. The frequencies of spermatocytes with various numbers and types of multivalents were used to estimate the proportions of sperm with normal, balanced translocated and unbalanced haploid genomes, and hence the expected frequencies of zygotes with abnormal karyo types. The expected frequency of semi-steriles (or translocation heterozygotes) in the progeny proved to be about twice as great as that observed in parallel genetic experiments (Lyon et al., 1964; Searle, 1964) and in the sons of the irradiated males. Expected dominant lethals were also about twice as frequent as observed by Lyon et al. Whatever assumptions are made regarding the distribution of chiasmata in the multivalents and their manner of disjunction, the observed frequencies of translocation heterozygotes or dominant lethals or both are much less than the expected frequencies. The evidence is considered to favour a selective process operating on diploid rather than haploid genomes but perhaps taking effect on the haploid spermatids or sperm.

ISSN:1424-8581    

DOI:10.1159/000130056

出版商:S. Karger AG    

年代:1969

数据来源: Karger

ISSN:1424-8581    

DOI:10.1159/000130057

出版商:S. Karger AG    

年代:1969

数据来源: Karger

ISSN:1424-8581    

DOI:10.1159/000130058

出版商:S. Karger AG    

年代:1969

数据来源: Karger

ISSN:1424-8581    

DOI:10.1159/000130059

出版商:S. Karger AG    

年代:1969

数据来源: Karger

ISSN:1424-8581    

DOI:10.1159/000130050

出版商:S. Karger AG    

年代:1969

数据来源: Karger