The evolutionary divergence and relationship of fishes is a complex and fascinating topic that is just beginning to be well understood. Genetic divergence during vertebrate evolution has been studied using a variety of methods. Most recent studies of evolutionary relationships among fishes have involved the use of gel electrophoresis. Genetic divergence and evolutionary relationship among animals as well as plants can be determined by gel electrophoresis. Individual polypeptides that differ by as little as a single amino acid can be resolved on a polyacrylamide gel based on their molecular weight. The banding pattern of proteins from one species of animal can be compared to another species to determine the genetic distance between the two species.
Many of the bands imaged on the gel are composed of several polypeptides linked together by disulfide bridges to form more complex proteins. The production of these proteins involves the interaction of several genes to form a functional unit. These proteins resist evolutionary change and are more conserved in nature than individual polypeptides.
In addition, muscle tissue is a functionally fixed structure that does not undergo much selection pressure through time. The banding pattern of your gel can show similarities that go further back in the evolution of the various fish species than can a gel that contains only individual polypeptides.
More than 70 million years ago, the first bony fish (teleosts) split into two major groups, the soft rayed fish and the spiny rayed fish. The soft rayed fish gave rise to the herrings, trout, salmon, and pikes. The spiny rayed fish gave rise to the perch, catfish, bass, and carp.
The perch is a small, shallow-water fish found in lakes, ponds, and slow-moving streams. It is easily recognized by the six to nine blackish bars on the sides of the body. When fully mature, it measures 4-12 inches in length and weighs only slightly more than one pound. The walleye has a mottled pattern with a black blotch at the posterior end. Although it belongs to the perch family, it can achieve a length of 30 inches and weigh up to 25 pounds. The salmon spends most of its adult life in the ocean; it returns to fresh water to spawn and die. It has a life span of 4 to 7 years and can reach a weight of up 70 pounds. Its physical characteristics include very small scales and a long posterior fin.
When students analyze their gel results, they should conclude that the yellow perch and walleye have a similar banding pattern because both are derived from a common ancestor only several million years ago, whereas the salmon banding pattern is quite different from either the walleye or perch.
EVOLUTIONARY RELATIONSHIP OF SOME COMMON FISH
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