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Biology: Dev Data for Phylogenetic Tree of Animals


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About this Lesson

  • Type: Video Tutorial
  • Length: 7:14
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 77 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: The Evolution of Life on Earth (34 lessons, $64.35)
Biology: Evolution of the Animal Kingdom (5 lessons, $9.90)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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Let's proceed with this idea of the animal phylogeny and let's get to a place where we're puzzled. Why are we puzzled? Well, as we take our animals in our room and start making a chart and saying, "Okay, this one is a parazoa. It has no true tissues, and all of these have true tissues," and then we make our little check marks and we say, "Aha! These have radial symmetry and these don't," but yet, we have these echinoderms, the starfish and sea urchins, and we put them with the bilaterally symmetrical ones. How could we do such a thing? A starfish is clearly not bilaterally symmetrical.
Well, we have a coincident divergence, too, and we have to look at that. And there's another diverging pattern that happens along with cephalization and bilateral symmetry versus radial symmetry, and that has to do with the embryology, and this is going to take preference, because the embryology is at the basis of our genetics. You and I both know that most of your genes are turned on as an embryo. So as we start to look at this phylogenetic tree, we have to start realizing that the genetics of the embryological development becomes very important.
And so an interesting thing also happened here. So I'm going to move this over so I can do some writing, but remember what we have. We have to the left a radially symmetrical group, and to the right, a bilaterally symmetrical group, but there's more to it than that. It turns out that there's a division according to the way the embryology of these organisms happen. Radial symmetry is diploblastic. I know, you don't know what that means. That's okay, I'm getting there. Bilateral symmetry is triploblastic.
What does this mean? Before I tell you what it means, what does that tell you about the echinoderms? What does that tell you about the starfish? Well, given the whole idea of the radial symmetry--but their radial symmetry must have developed later. They must come from a bilateral ancestor that developed radial symmetry later, and that's the beauty of this idea of derived versus ancestral traits. Since we are saying that the embryological development is the key ingredient here, then therefore, they must have developed radial symmetry later, because the first thing they had was a triploblastic embryo. So what does that mean? Good question. Let's talk about it.
Embryos develop from germ layers. You may have heard of some of these germ layers. Germ layers are the layers that give rise to tissue. It turns out that the organization of the germ layer is unbelievably important in what organs you end up with. It turns out that the radiata, the group we put off to the left there, have two germ layers, meaning that their embryo has two layers of cells--an outer layer and an inner layer, so that when we draw that we're going to have two cell layers of cells. Imagine that each of these is a cell. That is diploblastic.
On the other hand, bilateria, the right hand branch of that tree, has a triploblastic, and now you can probably figure out what that means. That means that it has three germ layers. And so now we're going to have actually three layers of cell. We have my purple layer of cells right here. And these layers, by the way, have names. We'll get to those in a second. So these three germ layers, as we're going to see at a later time, are actually going to have different fates. Each layer is going to form different organs, and they have names.
Well, with the two germ layers, our outer layer is called the "ectoderm," and our inner layer is called the "endo" or inner derm. Well, we're going to use the same terminology in our bilateria, so we're going to have ecto here, and endo there, but we have a middle layer, which is going to be the meso or middle derm. Now, all of this being said, you can imagine that it must be a much more complex picture than that. For example, what's going to be our next division? Well, remember what we just said? Here we have triploblastic. Here we have diploblastic. Well, now we get to a division that without more background on the way these embryos develop, we're going to be in trouble together here, because the thing of it is, is we're going to start talking about the type of body cavities we form. When we start talking about body cavities, we're talking about embryological development. So we're going to diverge a little bit and we're going to talk a little about embryological fertilization and development and the way these things develop so that the rest of the forks will be perfectly clear to you.
The Evolution of Life on Earth
Evolution of the Animal Kingdom
Developmental Data for the Phylogenetic Tree of Animals Page [1 of 1]

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