Fluorescent in situ hybridization of maize meiotic chromosomes as visualized by confocal microscopy.

Knob heterochromatin served as the model for the development of fluorescent chromosome in situ hybridization on maize meiotic chromosomes. The meiotic chromosomes were hybridized with a digoxigenin-labeled RNA probe of the knob repeat sequence that is a component of the morphologically determined knob heterochromatin. The fluorescein-labeled knob probe and propidium iodide counter-stained chromosomes were imaged using confocal laser scanning microscopy, which allowed for the individual analysis of each fluorescent probe emission intensity, the ability to utilize image processing techniques and the generation of high-resolution images. A composite, in register, merged image of the knob probe signal and meiotic chromosomes demonstrated exact co-localization of the knob probe and the morphologically identified knobs. The establishment of the fluorescent in situ hybridization technique in maize allows for the expanded study of the biological role of knob heterochromatin and the possibility of locating other repeat sequences on maize chromosomes.

Dual-channel continuous-flow system for determination of phenylalanine and galactose: application to newborn screening.

We describe a dual-channel AutoAnalyzer (Technicon) system for the simultaneous measurement of phenylalanine and galactose from blood specimens on filter-paper. Using a single 1/4-in.-diameter (6-mm) specimen, we measure both components fluorometrically at a rate of 70/h. Analytical recovery with the method and the linearity of measurements vs sample concentration are excellent through the ranges of interest, 0-200 mg/L for phenylalanine and 0-800 mg/L for galactose. Carryover at the critical values during screening, 40 mg/L for phenylalanine and 100 mg/L for galactose, is essentially zero. The dual-channel system provides the means to incorporate a low-incidence test, i.e., galactosemia (incidence 1/70 000), into an existing program for phenylalanine analysis, for which the higher rates (phenylketonuria, incidence 1/11 500) easily justify the cost of mass screening.