The Developmental Biology Journal Club Developmental Biology Tutorial Left-right Asymmetry OK, so symmetry isn't perfect. At first glance, the left and right sides of our bodies are identical to one-another. However, internally, some of our visceral organs are displaced to one side. The heart, for example, loops to the right side. This looping is consistent in the vertebrates and occurs very early in development.
Rare individuals have the opposite symmetry, which is known as situs inversus .
One way to begin studying this problem is to search for genes that are expressed early in development only on one side of the embryo and to formulate hypotheses on the origin and manifestation of handedness. Then experiments can be conducted to test these hypotheses. In fact, a number of asymmetrically-expressed genes have been discovered, and we are on our way toward understanding how handedness develops. The first gene that was discovered to have asymmetrical expression is Sonic hedgehog , which is expressed on the left side of the gastrulating chick embryo. The demonstration of asymmetrical patterns of expression of these genes has made it possible to investigate the relationships among them so that regulatory interactions among them could be determined.