Yesterday while reading recent posts on one of my Edmodo groups, I was introduced to a video called "The Birth and Death of Genes" which discussed a unique group of fishes - the icefish - which have white internal organs and clear (well, cloudy anyway) blood - no hemoglobin or red blood cells. These fishes were discovered near a remote island in the Antarctic Sea south of Africa in the 1920's and have been studied since then. In recent years, after the development of DNA gene sequencing technology, scientists have discovered the precise mutation in the hemoglobin gene that accounts for the unique "heme" protein which carries oxygen for the fish. They have subsequently determined the evolutionary significance of this - the mutated gene produces a sort of antifreeze for their blood which makes it possible for them to live and thrive in water temperatures well below the freezing point. This seems to be a mutation unique to this particular group of fishes. The video (only 13 minutes long) was really interesting, as are the classroom activities tied to it by HHMI - the Howard Hughes Medical Institute.
Isn't it amazing to think of the tiny little changes which add up over time to create the various differences between different organisms? This is one of the things I love about teaching and learning about evolution - how seemingly minute changes can make such a difference over time. One more miracle of life, which is what makes biology the most interesting of sciences!