Introduction: Fertilization
Fertilization is the process by which sex cells unite to form a zygote, or fertilized egg. Fertilization results in a new cell with a unique mix of genes. Sex cells (sperm or eggs) contain half the number of chromosomes normally found in the cells of an organism. Fertilization results in a complete set of chromosomes.
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Species-specific sea urchin fertilization
Sperm from the sea urchin species Lytechinus pictus are added to a mixed population of eggs from L. pictus (large eggs) and Strongylocentrotus purpuratus (small brown eggs). Only eggs from L. pictus are fertilized by the sperm.

Elapsed time about 3 minutes.
Sperm from the sea urchin species Lytechinus pictus were added to a mixed population of eggs from L. pictus (large eggs) and S. purpuratus (small brown eggs). Eggs were then immediately 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 20x DIC objective and digital camera.