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T Freedman

Publications and source records attributed to T Freedman.

9 recordsLinked to original sources
PubMed1997

A physical assay for meiotic recombination in Coprinus cinereus.

We have used the polymerase chain reaction (PCR) method to monitor meiotic recombination in the basidiomycete Coprinus cinereus. We used DNA-mediated transformation to recover strains with modifications of the trp1 locus. The modifications were designed to introduce unique PCR priming sites separated by a homologous 2.4 kb region in which crossing over could occur. We showed that exchange occurred in this region at the frequency expected for a typical region of this genome (2.4 kb should correspond to a genetic length of 0.08 cM). We also detected products resulting from crossing over in DNAs extracted from cells in meiotic prophase. The assay should be useful for monitoring exchange in mutants that cannot complete meiosis.

Blotting, Southern↗
PubMed1993

De novo methylation of repeated sequences in Coprinus cinereus.

We have examined the stability of duplicated DNA sequences in the sexual phase of the life cycle of the basidiomycete fungus, Coprinus cinereus. We observed premeiotic de novo methylation in haploid nuclei containing either a triplication, a tandem duplication, or an ectopic duplication. Methylation changes were not observed in unique sequences. Repeated sequences underwent methylation changes during the dikaryotic stage. In one cross, 27% of the segregants exhibited methylation-directed gene inactivation. However, all auxotrophs eventually reverted to prototrophy. C to T transition mutation were not observed in this study. Our studies also revealed one inversion that occurred in 50% of the segregants in a single triplication cross, and a single pop-out event that occurred during vegetative growth. These alterations were similar to changes reported in experiments with duplicated sequences in Neurospora crassa and Ascobolus immersus. However, significant differences were also noted. First, the extent of methylation was much less in C. cinereus than in the other two fungi. Second, CpG sequences appeared to be the preferred targets of methylation.

Ascomycota↗
PubMed1990

Industrial employee drug screening: a blind study of laboratory performance using commercially prepared controls.

Reference laboratories are an integral component of any industrial employee drug screening program. We evaluated the performance and accuracy of the reference laboratories used by Rockwell International, a large industrial employer with an active drug screening program. A total of 829 commercially prepared control samples containing drugs of abuse, over-the-counter drugs, and analytes found in the normal employee population were disguised as routine submissions to reference laboratories used by nine Rockwell facilities. Analyses of results included compilation of false-positive and false-negative errors per drug per laboratory and a correlation of errors with preliminary and confirmation methods. Error rates of 2% false-positive results and 20% false-negative results were found for all laboratories. The errors were not limited to any one technique nor to any particular drug. The error rates observed suggest the need for routine blind testing programs and increased interaction between industry and laboratories.

Animals↗
PubMed1987

Tempo and mode of sequence evolution in mitochondrial DNA of Hawaiian Drosophila.

Sequence comparisons were made for up to 667 bp of DNA cloned from 14 kinds of Hawaiian Drosophila and five other dipteran species. These sequences include parts of the genes for NADH dehydrogenase (subunits 1, 2, and 5) and rRNA (from the large ribosomal subunit). Because the times of divergence among these species are known approximately, the sequence comparisons give insight into the evolutionary dynamics of this molecule. Transitions account for nearly all of the differences between sequences that have diverged by less than 2%: for these sequences the mean rate of divergence appears to be about 2%/Myr. In comparisons involving greater divergence times and greater sequence divergence, relatively more of the sequence differences are due to transversions. Specifically, the fraction of these differences that are counted as transversions rises from an initial value of less than 0.1 to a plateau value of nearly 0.6. The time required to reach half of the plateau value, about 10 Myr, is similar to that for mammalian mtDNA. The mtDNAs of flies and mammals are also alike in the shape of the curve relating the percentage of positions at which there are differences in protein-coding regions to the time of divergence. For both groups of animals, the curve has a steep initial slope ascribable to fast accumulation of synonymous substitutions and a shallow final slope resulting from the slow accumulation of substitutions causing amino acid replacements. However, the percentage of all sites that can experience a high rate of substitution appears to be only about 8% for fly mtDNA compared to about 20% for mammalian mtDNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Mount Sinai Hospital's journey into TQM.

Toronto's Mount Sinai Hospital commenced its total quality management journey in the late 1980s as a complement to its extensive experience in quality assurance. This article focuses on Phase I--the process of setting up teams. This phase includes project nomination and selection; team membership selection and education; and the quality improvement process. The authors share the lessons they learned during the course of the journey and present the directions that TQM at Mount Sinai will take in the future.

Hospital Administration↗