Fig. 3. Freshly fertilized embryos of the sea urchin Strongylocentrotus droebachiensis after exposure to UVR at five different wavelengths (treatment groups). DNA damage was assessed by TUNEL-positive fluorescence, which reveals cells with DNA strand damage. See text for details. (A) 280 nm, (B) 305 nm, (C) 320 nm, (D) 375 nm, (E) 400 nm. Magnification 100x. (F) Single nuclei after 280 nm treatment; magnification 5500x.