Introduction: Sea Urchins
Sea urchins are spiny marine organisms; many different species are found in oceans around the world. Male and female individuals produce eggs and sperm that are shed freely into seawater. Scientists have long used the urchin as a model for studying fertilization and development.

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Sea urchin embryo abnormal mitosis
A sea urchin (Lytechinus pictus) embryo with stained DNA fails to undergo mitosis. This is likely due to DNA damage caused by a combination of the chemical used for staining and the light used to visualize the stain.

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Sea urchin embryos were fertilized and treated with Hoechst 3342 (a DNA stain), then mounted in seawater between a slide and coverslip (using a silicon spacer). Images were taken at room temperature on a compound inverted microscope using a 40x DIC objective DAPI filter set and digital camera. Both transmitted and fluorescent light sources were used.