Clones and Coin Flips at the Tide Pools

Low Tide at Driftwood Point

1Mateo Albuquerque's sixth-grade class took a field trip to the rocky shore at Driftwood Point during a very low tide. Their guide, marine biologist Dr. Rowan Kealoha, kept the group on the flat rocks, showed them how to touch animals with one gentle finger, and reminded them to leave every animal where they found it.

2Large rocks near the water were covered with aggregating anemones, small anemones that live packed together in patches. The anemones in one patch all looked alike, while neighboring patches had different colors. A strip of bare rock a few centimeters wide separated each patch from the next. Dr. Kealoha explained that an anemone of this kind can split itself in two from top to bottom, and each half becomes a complete anemone. A patch starts with one anemone that keeps splitting. In summer, the anemones also release eggs and sperm into the water. Fertilized eggs grow into tiny larvae that drift away and settle on new surfaces.

3Every three months, Dr. Kealoha photographs one marked square of rock, 50 cm on each side, inside Patch A, and counts the anemones. She also counted tentacle-tip colors in two rock patches and among young anemones that had settled on a new wooden pier post, built two years ago a short distance down the shore.

4Back in class, Mateo modeled a cross for one trait in a made-up tide pool snail. In his model, one gene controls the shell pattern: the allele B (banded) is dominant and the allele b (plain) is recessive. Both parents are Bb. To make one offspring, he flipped two coins, one for each parent: heads gave the allele B and tails gave b. He made 40 offspring this way.