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991.
Summary Testicular histology and meiosis has been studied in an XYY male patient identified at an infertility clinic. This man was found to have an XYY sex chromosome complement in 15% of spermatogonial metaphases. There was no clear evidence of 2 Y chromosomes at diakinesis but there appeared to be a slight excess of sperm with a fluorescent Y body. 相似文献
992.
We examined spleen cells from newborn to 1-month-old rabbits for easily detectable surface immunoglobulin, complement receptors, and for in vitro proliferative responsiveness to anti-immunoglobulin antisera and several mitogens. From birth through the first month of life about 15% of the cells from rabbit spleens had easily detectable surface immunoglobulin while about 45% had C3 receptors. In adults as many as 77% of the spleen cells had easily detectable surface Ig but the proportion with C3 receptors remained about 45%. The proliferative response to anti-allotype antisera was present at birth, and was at adult levels by 1 month of age. The proliferative response to pokeweed mitogen was low when cells were obtained during the first week of life but was comparable in magnitude to the response of adult cells by 2 weeks of age. In vitro responsiveness to concanavalin A was present at low levels at birth and increased sharply during the first week. We did not observe significant stimulation of spleen cells from neonatal to 4-week-old rabbits by lipopolysaccharide from Salmonella typhosa. Our data suggest that lymphocyte surface markers and functional responses appear asynchronously in spleen cells of developing rabbits. 相似文献
993.
V D Michaelis I Neumann B Schulz W Nowak W K?cher R Michael P Heinke R Reding 《Endokrinologie》1975,64(3):257-268
In 8 female patients carbohydrate tolerance was proved by means of glucose infusion test 3 days after cholecystectomy. Parameters analyzed in portal and peripheral vein blood are compared with that of 47 healthy persons. All patients demonstrate a pathological carbohydrate tolerance after cholecystectomy, further characterized by an increased lipolysis, a paradoxical rise of HGH, a diminished insulin secretion during the early and increased IRI output in the second phase. There is a significant positive correlation between portal and peripheral vein IRI concentration despite the rising portalperipheral venous IRI difference with raised portal venous IRI concentration. Corresponding differences for proinsulin concentrations can be established in the early phase only. Relations existing between blood glucose and IRI are shown by multiple regression analysis. They suggest that the altitude of IRI concentration is determined by previous blood glucose concentration. 相似文献
994.
Causes and consequences of Robertsonian exchange 总被引:11,自引:2,他引:9
At least two types of Robertsonian exchange are now known in the acrocentric chromosomes of man. Both types involve breakage in the arms adjacent to the centromere. Evidence is presented for a third type of exchange, one involving breakage within the centromere itself, in the grasshopper Percassa rugifrons. In this species, which is regularly homozygous for a single fusion metacentric, the eighteen rod autosomes have small but pronounced granules at the centric end of the chromosome. When C-banded these granules show differential Giemsa staining and appear to represent centromeric chromomeres; these chromomeres are lacking in the metacentric fusion product. Equivalent fusions may have occurred in some mammal species too and possible examples of this are discussed in sheep and mice. The Percassa fusion has led to a modification in both the frequency and the distribution of chiasmata as judged by a comparison of these properties in the metacentric relative to the two next smallest rod equivalents. Comparable modifications are known to occur in other naturally occurring fusions but these changes are certainly not automatic consequences of fusion since they are not shown in at least some newly produced fusion mutants. 相似文献
995.
Roy W. Keenan Michael Kruczek Lynn Fusinato 《Archives of biochemistry and biophysics》1975,167(2):697-705
Cell-free preparations from Tetrahymena pyriformis catalyze the incorporation of glucose from UDP-glucose into a glucolipid having properties which are identical to those of other dolichyl phosphoryl sugar derivatives. Kinetic and other experiments have provided evidence that this glucolipid serves as glucose donor for two other types of glucosylated substances, one of which has been tentatively identified as an oligosaccharide lipid and the other a glycoprotein or glycoproteins. In addition, the partially purified glucolipid served as a glucosyl donor to these cell components, suggesting that in this protozoan, at least part of the glycoprotein is synthesized by reactions involving lipid-linked sugars in a manner analogous to that which has been observed in glycoprotein synthesis in mammalian cells. 相似文献
996.
Michael E. McMahon Paul A. Hartman Robert A. Saul Lois H. Tiffany 《Applied microbiology》1975,30(1):103-109
Two small, leaky silos were filled with normal high-moisture corn (HMC), and two with HMC severely infested by Helminthosporium maydis. Counts of mesophilic bacteria, lactobacilli, coliforms, yeasts, and molds were made on corn samples as received and periodically thereafter during 220 days of storage. Temperature and gas levels also were monitored. Sequential changes in the populations of lactobacilli, yeasts, and molds were determined during spoilage of HMC. These population changes were compared on the basis of the variables encountered in the present study as well as with the results of previous studies conducted on normal HMC stored under adequate conditions. Heavy infestation by H. maydis had no appreciable effect on HMC preservation. 相似文献
997.
Sulfated glycosaminoglycan (GAG) synthesis by primary cultures of embryo, yolk sac, and trophoblast was compared with synthesis by the same tissues in utero. In general, the in vivo and in vitro results were in good agreement. As was the case in vivo, the three tissues synthesized chondroitin-4-sulfate and chondroitin-6-sulfate (but no dematan sulfate) at characteristic ratios.Cultured embryos are already capable of synthesizing chondroitin sulfates, primarily chondroitin-4-sulfate, before, or at, the 64-cell stage. During the attachment and initiation of outgrowth stages, blastocysts synthesize more chondroitin-6-sulfate than chondroitin-4-sulfate. Thereafter, progressively more chondroitin-4-sulfate is synthesized so that the 4:6 ratio increases, resembling that of trophoblast cells.Blastocyst-derived cell lines and teratoma cell cultures were also studied. One blastocyst-derived line, MB4, synthesized GAG with a pattern similar to that of yolk sac, which it resembles biochemically in other respects as well. The GAG profile of MB2, a parietal endoderm-like cell line resembled neither that of embryo, yolk sac, nor trophoblast cells. Embryonal carcinoma (undifferentiated teratoma) cells had a chondroitin sulfate pattern different from that of most of the other cultures. 相似文献
998.
999.
Repression of Diaminopimelic Acid Decarboxylase in Escherichia coli: Gene Dosage Effects and Escape Synthesis 总被引:1,自引:1,他引:0 下载免费PDF全文
Gene dosage and escape synthesis experiments support the hypothesis that diaminopimelate decarboxylase repression by lysine involves a repressor molecule in a negative control system. 相似文献
1000.
The ultrastructure of chloroplasts from 28 of the 73 species of Caulerpa Lamouroux (Chlorophyta, Caulerpales) has been studied to aid in interpreting phylogenetic relationships among the 12 recognized sections. Variations of systematic value include pyrenoid occurrence and fine structure, thylakoid architecture and amount of photosynthate storage. Comparisons of field and culture specimens indicate these characters are consistent. Chloroplast thylakoids are grouped into bands, with the distribution of bands differing among species. In the most common arrangement, bands are evenly distributed throughout the chloroplast. A few species show lateral displacement of bands whereas others have a majority of bands arranged at one end of the chloroplast. Starch is stored cither as one or two large grains (> 1 μm diam.) or numerous small grains (< 0.5 μm diam.). Electron-transparent regions are common in other species in which chloroplasts rarely store starch. Simple, embedded pyrenoids are present in several species of section Sedoideae. An opaque region occurs in chloroplasts of C. elongata which may represent an intermediate stage in the evolutionary loss of the pyrenoid. It is suggested that the chloroplast of Caulerpa evolved, from a large, complex, pyrenoid-containing organelle housing both photosynthetic and amylogenic functions, to a small, structurally simpler one, specialized for photosynthesis alone. A phylogeny of the 12 sections of Caulerpa is constructed, based on chloroplast evolution which agrees with an earlier morphology-based hypothesis on the origin and evolution of Caulerpa. 相似文献