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Biomedical subjects

John S Parker

Publications and source records attributed to John S Parker.

12 recordsLinked to original sources
PubMed2006

Cloning and characterization of dispersed repetitive DNA derived from microdissected sex chromosomes of Rumex acetosa.

Rumex acetosa is characterized by a multiple chromosome system (2n = 12 + XX for females, and 2n = 12 + XY1Y2 for males), in which sex is determined by the ratio between the number of X chromosomes and autosome sets. For a better understanding of the molecular structure and evolution of plant sex chromosomes, we have generated a sex chromosome specific library of R. acetosa by microdissection. The screening of this library has allowed us to identify 5 repetitive DNA families that have been characterized in detail. One of these families, DOP-20, has shown no homology with other sequences in databases. Nevertheless, the putative proteins encoded by the other 4 families, DOP-8, DOP-47, DOP-60, and DOP-61, show homology with proteins from different plant retroelements, including poly proteins from Ty3-gypsy- and Ty1-copia-like long terminal repeat (LTR) retroelements, and reverse transcriptase from non-LTR retro elements. Results indicate that sequences from these 5 families are dispersed throughout the genome of both males and females, but no appreciable accumulation or differentiation of these types of sequences have been found in the Y chromosomes. These repetitive DNA sequences are more conserved in the genome of other dioecious species such as Rumex papillaris, Rumex intermedius, Rumex thyrsoides, Rumex hastatulus, and Rumex suffruticosus, than in the polygamous, gynodioecious, or hermaphrodite species Rumex induratus, Rumex lunaria, Rumex con glom er atus, Rumex crispus, and Rumex bucephalo phorus, which supports a single origin of dioecious species in this genus. The implication of these transposable elements in the origin and evolution of the heteromorphic sex chromosomes of R. acetosa is discussed.

Amino Acid Sequence↗
PubMed2004

Asexual populations of the invasive weed Oxalis pes-caprae are genetically variable.

Oxalis pes-caprae, a native of South Africa is a very successful, globally widely distributed, aggressive colonizer weed. It spreads vegetatively (through bulbils and underground shoots) in most of its colonized areas. In Israel, it is characterized by the total lack of seed set. Using 121 amplified fragment length polymorphism (AFLP) putative loci we have analysed the genetic structure of five representative populations in Israel. Despite the complete lack of sexual reproduction and the total dependency on vegetative dispersal, populations were found to be genetically variable. Surprisingly, considerable genetic diversity was found within and between all of the populations tested. We speculate that this diversity could be the result of an accumulation of mutations or genome rearrangement.

Analysis of Variance↗
PubMed2003

A phase III, multicenter, randomized, placebo-controlled clinical trial of topical aminocaproic acid (Caprogel) in the management of traumatic hyphema.

OBJECTIVE: To determine the safety and efficacy of topical aminocaproic acid (Caprogel) in the management of traumatic hyphema. DESIGN: Multicenter, randomized, double-masked, placebo-controlled clinical trial. PARTICIPANTS: A total of 51 patients participated in this trial (power = 36%, 2-tailed test). INTERVENTION: Patients presenting with traumatic hyphema were randomly assigned to 5-day treatment with topical aminocaproic acid or a placebo gel. Patients were monitored daily with ocular examination and vital sign testing for the 5 days of treatment and at 24 and 48 hours after treatment. General physical examination and laboratory testing were performed at baseline and day 5. MAIN OUTCOME MEASURES: The main efficacy variable was the rate of rebleeding. Secondary efficacy variables included time to hyphema clearance, intraocular pressure, time to secondary hemorrhage, and visual acuity. Safety variables included adverse events, vital signs, and laboratory measurements. RESULTS: Rebleeding occurred in 30% of the placebo group (8 of 27; 95% confidence interval [CI] = 14-50%), versus 8% of the treatment group (2 of 24; 95% CI = 1-27%), for an estimated continuity-corrected difference in percentage of patients with bleeding of 17% (95% CI = -3-38%). Secondary efficacy variables were similar in the groups, except that there was a trend towards more visual improvement in the topical aminocaproic acid group (54%) than in the placebo group (30%) at the last measurement (P = 0.08). Adverse events were similar. CONCLUSIONS: This study provides evidence that topical aminocaproic acid is safe and demonstrates trends towards reducing the rebleeding rate in the management of traumatic hyphema. However, because the study was terminated before complete enrollment, more definitive recommendations will require a larger trial.

Administration, Topical↗
PubMed2003

Detection and effects of a homeologous reciprocal transposition in Brassica napus.

A reciprocal chromosomal transposition was identified in several annual oilseed Brassica napus genotypes used as parents in crosses to biennial genotypes for genetic mapping studies. The transposition involved an exchange of interstitial homeologous regions on linkage groups N7 and N16, and its detection was made possible by the use of segregating populations of doubled haploid lines and codominant RFLP markers. RFLP probes detected pairs of homeologous loci on N7 and N16 for which the annual and biennial parents had identical alleles in regions expected to be homeologous. The existence of an interstitial reciprocal transposition was confirmed by cytological analysis of synaptonemal complexes of annual x biennial F1 hybrids. Although it included approximately one-third of the physical length of the N7 and N16 chromosomes, few recombination events within the region were recovered in the progenies of the hybrids. Significantly higher seed yields were associated with the parental configurations of the rearrangement in segregating progenies. These progenies contained complete complements of homeologous chromosomes from the diploid progenitors of B. napus, and thus their higher seed yields provide evidence for the selective advantage of allopolyploidy through the fixation of intergenomic heterozygosity.

Brassica↗