Your Inner Fish Chapter 3

Scientists have been wondering that what kind of cells in our body is responsible for making our body characteristics look different. The researchers started by observing chicken eggs and the embryos. They moved around tissues to see if different changes occur in the characteristics.

As a result, scientists discovered the mirror-image duplication. They removed a tissue to the other side of the limb of the chicken, and the fingers still grow normally. This explains that certain cells are capable of instructing others to form the structure of the body. This patch of tissue is called the zone of polarizing activity. (ZPA)

Later, scientists found that the gene capable of making body segment different from another is also present in fly. They named it hedgehog. Soon, it is uncovered that every limbed animal has the Sonic Hedgehog gene.

A scientists chose to do experiments on shark embryos since they are the first animals that have fins with skeletons. They are very distantly related to human beings. However, it is very difficult to obtain shark embryos; therefore, skates embryos are used instead. After experiments on such embryos, it is found that Sonic Hedgehog in these embryos were turned on and turned on in the patch of tissue at the back end of the fin, which matches the chicken and fly embryos. Through vitamin A treatment, the mirror-image fin is discovered in the embryos as well. Therefore, scientists found the gene that is responsible for making different segments in our limbs.