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J M Mason

Publications and source records attributed to J M Mason.

At least 73 records · Page 4Linked to original sources
PubMed1993

HLA-A/B haplotye frequencies among U.S. Hispanic and African-American populations.

HLA-A/B haplotype frequency tables were developed for U.S. Hispanic and African-American populations from data collected from paternity cases. Two Hispanic tables were developed; one was based on data from Hispanics in the northeast U.S. and Florida and designated the Caribbean table whilte all other Hispanics were included in a table designated the Mexican table. The total number of individuals whose haplotypes were included in the Caribbean, Mexican, African-American tables was 1635, 2230, and 3134, respectively. Statistical comparisons were made of haplotype frequencies among these tables and tables previously reported.

Black or African American↗
PubMed1993

The genomic organization of HeT-A retroposons in Drosophila melanogaster.

Members of the Drosophila HeT-A family of transposable elements are LINE-like retroposons that are found at telomeres and in centric heterochromatin. We recently characterized an active HeT-A element that had transposed to a broken chromosome end fewer than nine generations before it was isolated. The sequence arrangement of this element, called 9D4, most likely represents the organization of an actively transposing member of the HeT-A family. Here we assess the degree of divergence among members of the HeT-A family and test a model of telomere length maintenance based on HeT-A transposition. The region containing the single open reading frame of this element appears to be more highly conserved than the non-coding regions. The HeT-A element has been implicated in the Drosophila telomere elongation process, because frequent transpositions to chromosome ends are sufficient to counter-balance nucleotide loss due to incomplete DNA replication. The proposed elongation model and the hypothetical mechanism of HeT-A transposition predict a predominant orientation of HeT-A elements with their oligo (A) tails facing proximally at chromosome ends, as well as the existence of irregular tandem arrays of HeT-A elements at chromosome ends resulting from transposition of new HeT-A elements onto chromosome ends with existing elements. Twenty-nine different HeT-A fragments were isolated from directional libraries that were enriched in terminal DNA fragments. Sequence analyses of these fragments and comparisons with the organization of the HeT-A element, 9D4, fit these two predictions and support the model of Drosophila telomere elongation by transposition of HeT-A elements.

Animals↗
PubMed1993

Fertility, reproduction, and genetic disease: studies on the mutagenic effects of environmental agents on mammalian germ cells.

Because genetically based diseases have a major impact on human health, the National Institute of Environmental Health Sciences (NIEHS) has conducted a research and testing program for more than a decade to address chemical induction of heritable genetic damage in the germ cells of mammals. Although most genetic disease results from preexisting mutations, a portion is due to the occurrence of new mutations. The supposition that exposure to mutagenic chemicals contributes to the occurrence of new mutations in the human population is strongly supported by the results from animal models. Such studies clearly demonstrate the potential of environmental chemicals to induce mutations in both somatic and reproductive cells of mammals. This NIEHS program has become a leader in the identification of genetic hazards in the environment and in the acquisition of animal model data used by regulatory agencies in assessing genetic risks to human health.

Animals↗
PubMed1993

Population screening for abdominal aortic aneurysm: do the benefits outweigh the costs?

To prevent the high mortality rate associated with ruptured abdominal aortic aneurysm (AAA), population screening at or soon after retirement age has been advocated, with elective operations being performed on patients with the appropriate indications. There is considerable pressure on some health authorities to fund such programmes even though there is substantial uncertainty about the consequent benefits. The ultrasound screening test is acceptable and accurate. Also, other health problems may be detected in the same screen. However, screening would lead to a questionable increase in surgery, as most patients with AAA die from other causes and not from a ruptured aneurysm. In addition, there is an elective operative mortality of around 5 per cent. Furthermore, as many of those who have a positive result on screening would never have known that they harbour an aneurysm, there is the possibility of unnecessary anxiety arising from the test. An economic analysis has been conducted for two identical, hypothetical cohorts of men using the best available data. One cohort was assumed to undergo screening and a number of men were indicated for immediate elective aneurysm repair or for follow-up, and surgery if their aneurysms become large. The other cohort was assumed not to be screened and would thereby face the possibility of rupture with its adverse outcome. The survival prospects of the two cohorts were calculated as life expectancies and in terms of life-years: the incremental life-years gained were compared with the incremental costs of the programme. Although there are considerable uncertainties in the analysis parameters, the base-line result and sensitivity analysis indicate that, on the basis of current knowledge, population screening should not be introduced.

Age Factors↗
PubMed1992

Chemical mutagenesis testing in Drosophila: VIII. Reexamination of equivocal results.

Twelve percent of the chemicals tested for mutagenicity by the National Toxicology Program (NTP) using the Drosophila sex-linked recessive lethal assay have been classified as producing equivocal results. We have reexamined the published data and the criteria used to determine mutagenicity in light of the historical distribution of the concurrent negative controls for this project. Many of the chemicals that originally produced equivocal results have been retested under code. As a result of changes to incorporate a comparison with the historical control in the algorithm used to determine mutagenicity and as a result of new data accumulated, 4 of the 25 chemicals that gave equivocal results are judged to be mutagenic, and 11 others are judged to be nonmutagenic under our test conditions.

Algorithms↗
PubMed1992

Frequent transpositions of Drosophila melanogaster HeT-A transposable elements to receding chromosome ends.

HeT-A elements are a new family of transposable elements in Drosophila that are found exclusively in telomeric regions and in the pericentric heterochromatin. Transposition of these elements onto broken chromosome ends has been implicated in chromosome healing. To monitor the fate of HeT-A elements that had attached to broken ends of the X chromosome, we examined individual X chromosomes from a defined population over a period of 17 generations. The ends of the X chromosomes with new HeT-A additions receded at the same rate as the broken ends before the HeT-A elements attached. In addition, some chromosomes, approximately 1% per generation, had acquired new HeT-A sequences of an average of 6 kb at their ends with oligo(A) tails at the junctions. Thus, the rate of addition of new material per generation matches the observed rate of terminal loss (70-75 bp) caused by incomplete replication at the end of the DNA molecule. One such recently transposed HeT-A element which is at least 12 kb in length has been examined in detail. It contains a single open reading frame of 2.8 kb which codes for a gag-like protein.

Amino Acid Sequence↗
PubMed1991

Aneuploidy in Drosophila, II. Further validation of the FIX and ZESTE genetic test systems employing female Drosophila melanogaster.

Two sensitive genetic systems for the detection of germline aneuploidy employing Drosophila melanogaster females were described in the first paper of this series (Zimmering et al., submitted to Mutation Research). Designated FIX and ZESTE, these systems permit the rapid and efficient detection of exceptional offspring derived from aneuploid female germ cells. The current report presents test results from a survey of 8 additional chemicals that have been analyzed in both systems. The tested chemicals include: acetonitrile, cadmium chloride, carbendazim, dimethylsulfoxide (DMSO), methylmercury(II) chloride, methoxyethyl acetate, propionitrile and water. Excluding the negative control, water, only the fungicide carbendazim failed to induce aneuploidy in either test system. Of the remaining 6 chemicals one, methylmercury(II) chloride, was positive in the FIX system but not in ZESTE, while MEA was positive in ZESTE and borderline in FIX. The results provide little evidence of germ-cell stage specificity of response to the tested chemicals. Comparison of the induced rates of aneuploidy i indicates that these can exhibit departures from simple additivity to the spontaneous rates: induced rates in the ZESTE system are generally higher and more variable than those from FIX. Possible reasons for the difference in responsiveness between FIX and ZESTE flies are discussed as is the question of the classification of those chemicals which induce chromosome loss events but not chromosome gains.

Acetates↗
PubMed1991

Strategy usage among deaf and hearing readers.

High school youths who were prelingually and profoundly deaf, hearing elementary-school-age youths, and hearing reading-disabled high school youths read expository texts and filled in deleted words and phrases. After making word replacements, they explained their decisions in sign or verbally. As expected, the hearing youths had an easier time filling in the deleted portions and explaining what strategies they were using. While the deaf youths reported using similar strategies as the hearing youths, the frequency of each type of strategy differed. Deaf readers more often relied on rereading and background knowledge, while the hearing readers made greater use of context clues. The results suggest that instruction for deaf readers should include more effective comprehension strategies.

Adolescent↗
PubMed1990

Addition of telomere-associated HeT DNA sequences "heals" broken chromosome ends in Drosophila.

Stocks of D. melanogaster X chromosomes carrying terminal deletions (RT chromosomes) have been maintained for several years. Some of the chromosomes are slowly losing DNA from the broken ends (as expected if replication is incomplete) and show no telomere-associated DNA added to the receding ends. Two stocks carry chromosomes that have become "healed" and are no longer losing DNA. In both stocks the broken chromosome end has acquired a segment of HeT DNA, a family of complex repeats found only at telomeres and in pericentric heterochromatin. Although the HeT family is complex, the HeT sequence joined to the broken chromosome end is the same in both stocks. In contrast, the two chromosomes are broken in different places and have no detectable sequence similarity at the junction with the new DNA. Sequence analysis suggests that the new telomere sequences have been added by a specific mechanism that does not involve homologous recombination.

Animals↗
PubMed1990

Recovery and characterization of hybrid dysgenesis-induced mei-9 and mei-41 alleles of Drosophila melanogaster.

X-Linked methyl methanesulfonate (MMS)-sensitive mutations were induced with hybrid dysgenesis using four P strains: pi 2, Harwich, T-007 and OK-1. Mutations were identified after two generations of backcrosses to M strain females to replace the autosomes. Among 51,471 X-chromosomes examined 10 carried stable MMS-sensitive mutations representing 8 independent events. Males of the mutant strains failed to induce gonadal dysgenesis in crosses to Oregon-R females at 28.5 degrees C. Complementation tests showed that 3 of the induced mutations were mei-9 alleles, 2 were mei-41 alleles, 1 was a mus102 allele, and 2 were alleles at a newly identified MMS-sensitive locus, mus112 (map position: 1-32.8). As assayed by in situ hybridization on polytene chromosomes, each X-chromosome had no more than four P element insertions. 4 of the 8 mutations recovered in this study proved to have P element insertions at or very close to sites to which MMS sensitivity has been mapped. Hybrid dysgenesis-induced reversion of 2 mutants, mei-9RT1 and mei-41RT2, is associated with the loss of the P element from regions 4B and 14C respectively.

Alleles↗
PubMed1990

Aneuploidy in Drosophila, I. Genetic test systems in the female Drosophila melanogaster for the rapid detection of chemically induced chromosome gain and chromosome loss.

An account is provided of two genetic schemes in the Drosophila melanogaster female designed as rapid detectors of chemically induced aneuploidy, including both chromosome gain and chromosome loss. One scheme is referred to as FIX, in which the female carried free (heterozygously) inverted X (chromosomes) and the other, ZESTE, where females do not carry inversions and the X-linked sexually dimorphic zeste mutation plays the key role in the detection of aneuploid offspring. The principle attribute of the FIX system is that all euploid offspring are wild-type for body and eye color whereas aneuploid females have a yellow body and aneuploid males white eyes; int he ZESTE system all euploid individuals are wild-type for eye color, aneuploid females possess zeste-colored eyes and aneuploid males white eyes. In addition induced polyploidies (2X:2A gametes) appear as yellow and zeste male intersexes in the FIX and ZESTE systems, respectively. In this way all aneuploids are recognized immediately. Consequently, detection of compounds with weak effects requiring large sample sizes may be made in a fraction of the time associated with more traditional schemes for aneuploidy detection in Drosophila.

Aneuploidy↗