You are a TA preparing for a sea urchin fertilization experi

You are a TA preparing for a sea urchin fertilization experiment. Two species are being used in the lab. You collect sperm and eggs from each species but forgot to label which species each of your samples came from. What experiment would you do to determine which sperm and egg samples came from the same species? What observations would you make in your experiment?

Solution

The fertilization of gametes in sea urchins is species specific meaning the sperm and the egg of the same species will only be attracted towards each other.This species - specific adhesion of the sperm to the egg is because of a specific protein called bindin and a complementary adhesion site in the egg;

This can be easily observed under the microscope.The sperm and the egg samples can be easily identified by their colour. The sperm sample will be whitish and the egg sample will be reddish.

Taking all precautions of handling the samples take a drop of the egg sample on a depressed glass slide and without dropping the coverslip observe under the microscope. You can see the eggs. Now carefully take a diluted drop of the sperm sample with a pippette and add it to the slide. If the sperm is from the same species there will be quick movement and adhesion of the sperm head to the receptor site of the egg.

If the sperm is from a different species there will be no attraction. Though the sperms move fast they will not get attached to the egg. This can be easily observed under the microscope.