New applications of laser microbeam irradiation to cell and developmental biology include a new instrument with a tunable wavelength (217- to 800-nanometer) laser microbeam and a wide range of energies and exposure durations (down to 25 × 10 -12 second). Laser microbeams can be used for microirradiation of selected nucleolar genetic regions and for laser microdissection of mitotic and cytoplasmic organelles. They are also used to disrupt the developing neurosensory appendages of the cricket and the imaginal discs of Drosophila .

Replication-defective mutants of herpes simplex virus type 1 (HSV-1) may prove useful as vectors for gene transfer, particularly to nondividing cells. CgalA3 is an immediate-early gene 3 (IE 3) deletion mutant of 2952

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A significant problem associated with cytogenetic prenatal diagnosis is distinguishing between true and pseudomosaicism. This becomes a diagnostic dilemma when fetal mosaicism corresponds with a known clinical entity. True mosaicism reportedly occurs with a frequency of 0.2 per cent and pseudomosaicism in 0.7 per cent to 2.7 per cent of cases. In the past 12 months, our laboratory has completed 522 fetal karyotypes. Nine cases were found to demonstrate mosaicism, 4 true mosaics (0.8 per cent) and 6 pseudomosaics (1.1 per cent). One case demonstrated both true and pseudomosaicism. In all cases of true mosaicism, the pregnancy was continued and karyotypes completed at birth. Our results demonstrate a danger of' rigid adherence to the criteria for true and pseudomosaicism in the examination of amniotic fluids. It is suggested that the criteria established for true and pseudomosaicism may not be valid when an aberrant cell line is found in a single flask and when that aberrant cell line is compatible with a known clinical entity due to a chromosome anomaly.

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