Modern genetics confirm ancient relationship between fins and hands

Source: University of Chicago Medical Center
Date Published: 22 December 2014
Authors: Andrew R. Gehrke, Igor Schneider, Elisa de la Calle-Mustienes, Juan J. Tena, Carlos Gomez-
Marin, Mayuri Chandran, Tetsuya Nakamura, Ingo Braasch, John H. Postlethwait, José Luis Gómez-Skarmeta, and Neil H. Shubin.
URL: http://www.sciencedaily.com/releases/2014/12/141222165441.htm

Summary:

With new genetic technology and machinery, researchers were able to finally continue the efforts to connect the evolutionary transition from fishes' fins to human wrists and fingers. At first they had fallen short, looking at the wrong fish, but now they have found the right one, the spotted gar, whose genome was recently sequenced. Paleontologists have documented the many pieces of evidence pointing to ancient lobbed-finned fish using the necessary adaptation to transform pectoral fins used underwater to strong, bony structures. Evolutionary biologists have however questioned why the  modern structure called the autopod--having wrists and fingers or ankles and toes have no obvious morphological counterpart in the fins of living fishes. Scientists combined the knowledge of fossil records and documents with genetic technology and machinery. Initial attempts to confirm the link based on shape comparisons of fin and limb bones were unsuccessful since autopod fins differ greatly with other fishes' fins. The primary genes that shape the bones, known as the HoxD and HoxA clusters, also differ. Researchers first tested the ability of the genetic "switches" that control HoxD and HoxA genes from teleosts (bony, ray-finned fish) to shape the limbs of developing transgenic mice. The fish control switches, however, did not trigger any activity in the autopod. They slowly begin to realize that teleosts were not greatest match to compare to how ancient genes were regulated. They found out the problem came from a change in the genetics of the fish about 300 million years ago. After the fish-like creatures that would become tetrapods split off from other bony fish, a common ancestor of the teleost lineage went through a whole-genome duplication (WGD)--a phenomenon that has occurred multiple times in evolution. By having their ancestor go through WGD, it made the potential for more diversity among the species. And over time different populations in different environments were able to adapt and some even under went genetic shuffling/drifting. The spotted gar, the fish that was said earlier in the article was one of the fish that did not undergo WGD, it split off of the teleost fishes before the WGD. When the research team compared Hox gene switches from the spotted gar with tetrapods, they found a high degree of similarity between "distal radials of bony fish and the autopod of tetrapods." Then to test further, they inserted the spotted gar gene switches related to fin development into developing mice. This evoked patterns of activity that were "nearly indistinguishable," the authors note, from those driven by the mouse genome."Overall," the researchers conclude, "our results provide regulatory support for an ancient origin of the 'late' phase of Hox expression that is responsible for building the autopod."

Relevance:

This article is relevant to the current unit we are studying because its all about the study of evolution, specifically the evolution from fish fins to human and other animal bony structures. It talks about the genome which also refers back to the last unit of molecular genetics we were learning and DNA/ gene extraction just like how they extracted the spotted gar gene switch and put it into developing mice. It talks about an event that happened over 300 million years ago on earth that had to do with complete genome copying. And that event also helped to create better diversity within the species which helped populations to adapt to their environments, such as Darwin's theory of natural selection.