Spontaneous X chromosome MI and MII nondisjunction events in Drosophila melanogaster oocytes have different recombinational histories.

Recent studies of human oocytes have demonstrated an enrichment for distal exchanges among meiosis I (MI) nondisjunction events and for proximal exchanges among meiosis II (MII) events. Our characterization of 103 cases of spontaneous X chromosome nondisjunction in Drosophila oocytes strongly parallels these observations. The recombinational histories of MI (97/103) and MII (6/103) nondisjunctional ova were strikingly different. MI nondisjunction occurred primarily in oocytes with non-exchange X chromosomes; of the new nondisjoining exchange bivalents, most carried distal crossovers. Thus, spontaneous MI nondisjunction reflects the failure of the achiasmate segregation systems. MII nondisjunction occurred only in oocytes with proximal exchanges. We propose several models to explain how very proximal exchanges might impair proper segregation.

Sensitivity and specificity of preoperative ultrasonography for diagnosing nodal metastases in patients with breast cancer.

PURPOSE: Rational therapy planning should aim to minimize the rate of axillary lymph node dissection (ALND) in patients without metastatic disease. By the same token, the frequency of sentinel lymph node biopsies (SLNB) should not be unnecessarily high in patients with axillary node disease. Preoperative axillary ultrasonography is a generally available noninvasive technique for assessing nodal status. MATERIALS AND METHODS: Based on retrospective data, we analyzed the sensitivity, specificity, positive and negative predictive value, and efficiency of preoperative ultrasonography US. A total of 429 axillary ultrasonographic examinations were included, and the management decisions were based on the ultrasonographic findings. Patients with suspicious US results were scheduled for ALND, while patients with unremarkable findings underwent SLNB. RESULTS: Axillary metastases were found in 146 of 429 (34 %) cases. In 75 of 429 (17 %) axillary examinations, ultrasonography revealed suspicious findings. In these cases, we proceeded with ALND, thereby reducing the number of SLNB by 17 %. 219 of 429 cases were classified correctly as not having metastasis, thus lowering the rate of ALND, which is associated with higher postoperative morbidity, by 51 %. Preoperative ultrasonography had a sensitivity of 53.6 %, specificity of 75.5 %, and a positive predictive value of 77.3 %. The negative predictive value was 51.3 % and the efficiency was 68.5 %. CONCLUSION: Ultrasonography is a moderately sensitive, but quite specific, preoperative method for assessing the axillary lymph nodes.

Measurement of 227Ac impurity in 225Ac using decay energy spectroscopy.

225Ac is a valuable medical radionuclide for targeted α therapy, but 227Ac is an undesirable byproduct of an accelerator-based synthesis method under investigation. Sufficient detector sensitivity is critical for quantifying the trace impurity of 227Ac, with the 227Ac/225Ac activity ratio predicted to be approximately 0.15% by end-of-bombardment (EOB). Superconducting transition edge sensor (TES) microcalorimeters offer high resolution energy spectroscopy using the normal-to-superconducting phase transition to measure small changes in temperature. By embedding 225Ac production samples in a gold foil thermally coupled to a TES microcalorimeter we can measure the decay energies of the radionuclides embedded with high resolution and 100% detection efficiency. This technique, known as decay energy spectroscopy (DES), collapses several peaks from α decays into single Q-value peaks. In practice there are more complex factors in the interpretation of data using DES, which we will discuss herein. Using this technique we measured the EOB 227Ac impurity to be (0.142 ± 0.005)% for a single production sample. This demonstration has shown that DES is a useful tool for quantitative measurements of complicated spectra.

Tales from the front lines: the creative essay as a tool for teaching genetics.

In contrast to the more typical mock grant proposals or literature reviews, we describe the use of the creative essay as a novel tool for teaching human genetics at the college level. This method has worked well for both nonmajor and advanced courses for biology majors. The 10- to 15-page essay is written in storylike form and represents a student's response to the choice of 6-8 scenarios describing human beings coping with various genetic dilemmas. We have found this tool to be invaluable both in developing students' ability to express genetic concepts in lay terms and in promoting student awareness of genetic issues outside of the classroom. Examples from student essays are presented to illustrate these points, and guidelines are suggested regarding instructor expectations of student creativity and scientific accuracy. Methods of grading this assignment are also discussed.

Human aneuploidy: lessons from achiasmate segregation in Drosophila melanogaster.

Aneuploidy is a crucial issue in human reproductive biology, accounting for both a significant proportion of miscarriages and, among liveborns, multiple congenital malformation syndromes such as Down Syndrome. Although the etiology of human aneuploidy remains poorly understood, recent studies have elucidated certain fundamental correlates of meiotic nondisjunction, such as altered recombination. These features are extraordinarily similar to those associated with chromosome misbehavior in Drosophila melanogaster females. Furthermore, these organisms also share a significant level of achiasmate chromosome nondisjunction. Here we describe in detail the processes of achiasmate chromosome segregation in Drosophila and discuss how they may be most effectively applied to our understanding of the etiology of human aneuploidy. In particular, we examine the possibility that similar "backup" mechanisms of chromosome segregation might function in mammalian meiosis, particularly mammalian females. Drawing upon observations made in flies, we also propose a new model for the segregation of achiasmate chromosomes in humans.

Recombination and nondisjunction in humans and flies.

Recent studies of Drosophila and humans indicate that aberrant genetic recombination is an important component of nondisjunction in both species. In both, a proportion of nondisjunction is associated with failure to pair and/or recombine and in both, exchanges which are either too distal or too proximal increase the likelihood of malsegregation. In this review we provide two perspectives on these observations: first, a review of exchange and chromosome segregation in model organisms, focusing on Drosophila, and secondly an overview of nondisjunction in humans. This format allows us to describe the paradigms developed from studies of model organisms and to ask whether these paradigms apply to the human situation.