Search PubMed⌕ Search

Biomedical subjects

C C Li

Publications and source records attributed to C C Li.

At least 91 records · Page 5Linked to original sources
PubMed1986

A method of subdividing genetic data into self-contained subsets.

A method of subdividing genetic data into self-contained subsets has been described in terms of examples. The subsets are such that each of them permits a valid estimate of the parameter concerned. Hence, the discarding of one or more subsets would not affect the validity of the remaining data. The detailed statistical properties of such subsets await further investigation. There is a need to simplify the variance formulas for estimates based on partial data.

ABO Blood-Group System↗
PubMed1986

Inbreeding and the balance between selection and mutation.

The first half of the paper described the structure of a large population caused by subdivision and inbreeding. Then, in the second half, it shows the structure of a population does not play any role in determining the incidence of the recessive genotype (aa). The latter is determined entirely by the ratio of the mutation rate to the selection coefficient. The recessive gene frequency, however, depends much on the structure of the population. The effect of relaxing inbreeding and subdivision on the rise and fall (rather the fall and rise) of the recessive gene frequency has been discussed.

Gene Frequency↗
PubMed1985

Direct detection of the human papovavirus BK in urine of bone marrow transplant recipients: comparison of DNA hybridization with ELISA.

Urine specimens from bone marrow transplant (BMT) recipients and from controls were directly tested for BK virus (BKV) DNA sequences by dot hybridization and for BKV antigen by a double-antibody indirect ELISA. A total of 158 specimens from 55 BMT patients (57 collected prior to or at the time of transplantation and 101 in the posttransplant period) and single urines from 125 control subjects were examined by both methods. A molecularly cloned, 32P-labelled BKV probe was hybridized with urine sediments that were spotted directly on nitrocellulose filters and denatured in situ. BKV DNA sequences were detected in 1 (1.8%) pretransplant and 22 (21.8%) posttransplant urines of BMT patients, and in none of control urines. In ELISA of urine supernatants, BKV antigen was detected in 1 (1.8%) pretransplant and 21 (20.8%) posttransplant urines of BMT patients and in 1 (0.8%) of the control urines. The results of the two tests correlated as follows: 16 urines were positive and 253 urines negative by both methods; seven specimens were positive by DNA hybridization only and seven were positive by ELISA alone. Virus excretion in urine was demonstrated in 20 (36.4%) patients by DNA hybridization, in 19 (34.5%) patients by ELISA, in 15 (27.3%) patients by both methods, and in 24 (44%) patients by at least one of the two tests.

Adolescent↗
PubMed1985

Some epidemiologic observations of nasopharyngeal carcinoma in Guangdong, People's Republic of China.

Chinese in the province of Guangdong have the highest risk of nasopharyngeal carcinoma (NPC) in China. Within Guangdong, variation in rates among the 3 major dialect groups is threefold. The Cantonese who reside in the central region of Guangdong display the highest risk of NPC. Among the Cantonese, those living on boats have twice the risk of those who live on land. These observations are consistent with earlier studies of southern Chinese residing in Hong Kong and Southeast Asia.

China↗
PubMed1985

Basic fallacies in the formulation of the paternity index.

Some basic fallacies in the computation of the paternity index have been pointed out. The general finding that the true fathers' mean paternity index is greater than that of nonfathers is a necessary consequence of an algebraic identity, having nothing to do with paternity or nonpaternity. It has also been shown that the paternity index is not a likelihood ratio as claimed. The fact that a paternity index may frequently take values less than unity leads to absurd conclusions regarding the probability of paternity. A formula relating prior and posterior probabilities of paternity, based solely on genetic marker testing results (exclusion or nonexclusion), is reiterated as a substitute for the current paternity index.

Humans↗
PubMed1983

Glycerol transport and phosphorylation by rat hepatocytes.

The entry of glycerol into isolated rat hepatocytes appears to be catalyzed by a specific carrier. At a physiological concentration of 0.1 mM, glycerol utilization is rate limited by the permeation step. Intracellular glycerol is trapped by an excess of glycerol kinase, which has a higher apparent affinity for the substrate than that of the membrane carrier. The entry of glycerol into the hepatocytes is highly sensitive to inhibition by monoacetin and cytochalasin B, but not by DL-1,2-propanediol, erythritol, D-glucose, D-galactose, D-mannose, or D-fructose.

Animals↗
PubMed1982

Molecular cloning, genomic analysis, and biological properties of rat leukemia virus and the onc sequences of Rasheed rat sarcoma virus.

Rasheed rat sarcoma virus (RaSV) has been shown to code for a protein of 29,000 Mr not present in replication-competent rat type C helper virus (RaLV)-infected cells. This protein is a fused gene product consisting of a portion of the RaLV p15 gag protein and the transformation-specific 21,000 Mr (p21) ras protein, which is also found in Harvey murine sarcoma virus. We now report the molecular cloning of both the SD-1 (Sprague-Dawley) strain of RaLV and the transforming ras sequences of RaSV. Heteroduplex analysis of these cloned DNAs demonstrated that the RaSV ras gene (v-Ra-ras) was inserted into the rat type C viral genome with a small deletion of RaLV genetic information in the 5' region of the gag gene and that the v-Ra-ras gene (0.72 kilobase pair) is homologous to and colinear with the p21 ras gene of Harvey murine sarcoma virus (v-Ha-ras). Restriction enzyme mapping confirmed the homology demonstrated by heteroduplex mapping, showing strong site conservation of restriction endonucleases known to cleave v-Ha-ras. Cloned v-Ra-ras DNA transformed NIH 3T3 cells, inducing the synthesis of the p29 RaSVgag-ras protein.

Base Sequence↗
PubMed1978

The selection of a stable rat hepatoma variant with concomitant increase in ploidy and permeability to glycerol.

By repeated selection for longer survival in an isotonic solution of glycerol, a stable subline of Novikoff rat hepatoma cells has been isolated. The cells exhibit markedly increased resistances to osmotic lysis in isotonic solutions of glycerol. They are twice as large and have twice as many chromosomes as cells of the parental line. It is suggested that the osmotic stress procedure can be extended for the selection of numerous kinds of mutants and can be used as a method of analysis of membrane properties.

Animals↗
PubMed1978

On measuring genetic distance by selection intensity.

A simple selection model (fitness 1, w, w2 for AA, Aa, aa) is employed to change the gene frequency of one population to another. The genetic distance is then defined as d = -log w between the two populations. The distance is symmetrical with respect to the two populations. It is additive: d13 = d12 + d23. The sampling variance of d takes a very simple form. The possible difficulties of using genetic distance in studying evolutionary history have been briefly discussed. The writer means no offence to those who have developed or used the various measures of genetic distance.

Gene Frequency↗
PubMed1976

Transport mechanisms in isolated plasma membranes. Nucleoside processing by membrane vesicles from mouse fibroblast cells grown in defined medium.

Plasma membrane vesicles were isolated from a subline of L929 mouse fibroblasts grown on defined medium in the absence of serum. These vesicles were not significantly contaminated by mitochondria or endoplasmic reticulum. The isolation procedure, a modification of that originally developed by McKeel and Jarett (McKeel, D.W., and Jarett, L. (1970) J. Cell Biol. 44, 417-432) employs mechanical homogenization in isotonic medium followed by differential centrifugation. The resultant plasma membrane vesicles take up radioactivity when exposed to uniformly labeled nucleosides. Two subfractions of the plasma membrane were isolated, distinguished by their differing activity of 5'-nucleotidase and (Na+,K+)-stimulated ATPase, two well known plasma membrane enzyme markers. Uptake of nucleoside radioactivity was extensively studied in one subfraction; it was linear with time and membrane concentration over ranges used for the studies. Apparent Km values for uptake of radioactivity from adenosine, inosine, and uridine were 7.1 +/- 26 muM, respectively. Uptake of radioactivity from all three nucleosides exhibits a broad pH optimum from pH 7 to pH 9, but falls off rapidly at lower pH. N-Ethylmaleimide was an effective inhibitor of uptake of radioactivity from all three nucleosides; uptake of radioactivity from uridine is more sensitive than uptake of radioactivity from the purine nucleosides. Adenosine inhibited uptake of radioactivity from inosine more than from uridine. Inosine inhibited the uptake of radioactivity from adenosine, but uridine did not. Caffeine and 6-methylaminopurine riboside (6-N-methyladenosine differentially inhibit uptake of radioactivity from adenosine and inosine, and thus the vesicles apparently possess seperate transport systems for uptake of radioactivity from purine nucleosides and from uridine.

Adenosine Triphosphatases↗
PubMed1976

Membrane-associated enzymes involved in nucleoside processing by plasma membrane vesicles isolated from L929 cells grown in defined medium.

adenosine, adenosine,Transport-competent plasma membrane vesicles isolated from a subline of L929 cells (L929se-) grown in serum-free, defined medium accumulate ribose-1-P when exposed to adensoine, inosine, guanosine, or uridine. This observation suggests the action of one or more nucleoside phosphorylases acting prior to, during, or subsequent to the transport event. Extravesicular ribose-1-P neither inhibits uptake nor exchanges with intravesicular ribose-1-P, indicating that the action of the phosphorylase is not prior to uptake. Preloading the vesicles with inosine prior to subjecting the vesicles to conditions under which further uptake could not take place (in the presence of caffeine) did not result in an alteration of the ribose-1-P to inosine ratio within the vesicles. This observation was interpreted as evidence that only exogenously derived, not intravesicular inosine, is the substrate for the nucleoside phosphorylase. This datum, when taken with the fact that hypoxanthine is never found to be a significant extent within the vesicles, suggests that the phosphorolytic cleavage of inosine occurs as a group translocation during the transport itself, so that hypoxanthine is released to the surrounding medium while the ribose-1-P accumulates intravesicularly. Thus, phosphorolysis would seem to occur during passage across the membrane.

Adenosine Deaminase↗