Chapter+06


 * Q: Shubin discusses several different experiments during this chapter, focusing especially on those of Mangold. Why were her experiments so revolutionary and what was her most important discovery? (I. Perler) **

The outer layer is called the ectoderm, the inner layer is called the endoderm, and the middle layer is called the mesoderm. The ectoderm forms much of the outer body (the skin and nervous system). The endoderm forms the inner structures (the digestive tract and other glands that deal with that). The mesoderm forms the tissues between the guts and the skin ( the skeleton and muscles). This is advantageous more for scientists to help track evolution and study evolution. Since most vertebras have the same embryonic structure, the scientist can track the route of change through this. It helps scientist find genes like the //Hox Gene// and the //Noggin Gene.// (J. Speelman)
 * Q: Shubin spends a lot of time discussing how embryonic development is classified into three parts or layers. What are these parts and why is it advantageous enough for almost all animals to have them in common while developing? (M. Blanchard)**

A: Noggin is a gene that is responsible for the development of the body axis/back structures as well as other organs. If this gene is mutated, then there could be defects in the development of the body axis that would lead to deformities. Also, if the Noggin gene were to be mutated, then the DNA wouldn't be correctly transcribed in order to produce the right amino acids that would in the end, produce an incorrect protein. (T. Gebhart)
 * Q: Richard Harland was doing experiments dealing with the Organizer, and discovered a gene called, the //Noggin.// Explain what the purpose of this gene is and what would you expect to happen if the //Noggin// gene is mutated? (J. terHorst)**

A: The Noggin is a gene that when injected acts as an organizer and caused the embryos to develop two body axes. Noggin develops the body axes and is involved with the host of other organs. If Noggin is mutated, it could cause more than two body axes to develop or maybe only one. This would result in deformities and many issues with the accompanying organs and body structures that form and function around these axes. (M. McKinney) A: While we have different forms of symmetry( Bilateral V. Radial), there are still symmetrical properties( axes of symmetry) and directional orientations in both humans and sea anemones. These are seen in concepts such as head-anus body structure, and a concept of "front and back" which is one of the axes of symmetry. The point that Shubin is making here is that those animals such as the sea anemones have a very primitive stricture of what we deem a "body", and while very outdated by our standards, our beginnings of building our bodies can be traced back to them(C.King)
 * Q: Humans have what is called bilateral symmetry while sea anemones have what is called radial symmetry. But it is said that our body plans are still very similar, what does this mean? ( A. Schmidt)**

The genes that most animals have to control body organization are //Hox// genes. The experiment focused on mutant flies with organs in the wrong places, which must have been a result of an error in their DNA. These flies were bred to make a whole population with this genetic mutations, and molecular markers were used to compare the genes of flies with the mutation to those without in order to pinpoint the region of the chromosome responsible for the mutant effect. It was found that these genes were next to each other on one of the long DNA strands of the fly, in order from those controlling the front end to the rear part of the fly. The middle of each gene had a short DNA sequence (homeobox) that was basically the same in every species that was observed. The genes that contain this homeobox are called //Hox// genes, and they control body organization. These genes are beneficial because they provide a plan for an organism to develop and establishes the proportions of our bodies. If there are problems with these genes, things can go very wrong. For example, if the Hox genes are mixed up, limbs could be missing. This would keep the organism from fully functioning, and it would be unable to move as fast or capture prey as well, so it would be out-competed and die, unable to pass its genes to the next generation. With these genes, limbs and organs line up in the proper places so that organisms can have a better chance to compete for resources, survive, and pass on their genes to the next generation (A. Nolan).
 * Q: What is the name of the gene that most animals have that controls body organization? Explain the experiment that was done on fruit flies that identified these genes and how they are evolutionary beneficial to organism development. (C. Nikolai).**


 * Q: Based on what Shubin said about axes on both mammals and sea creatures such as jellyfish, corals, and sea anemones, about how long ago was our common ancestor? Explain. (L. Bentley)**

A. Shubin found that when he grafted a piece of tissue off the embryo onto another embryo, he could produce twins. The information located here was DNA. In order for the two embryos to develope into twins, they would have to undergo many sets of mitosis. Starting with a single cell, the DNA located in that Organizer would be replicated over and over, creating new cells and creating identical babies. (E. Olson)
 * Q: Explain the results of Spemann's experiment. What was the "information" located in the nucleus. Using what we have learned this year, describe the process the embryo went through to produce the end result in Spemann's experiment. (R. Heis)**

A: The common developmental pathways of organisms supports the idea of a common ancestor in animals. In all three types of animals, the same or similar structures are all derived from the same portions of the developing embryo. The major example used in this book is the changes in the structure and function of the gill arches. While the derived structures may appear very different in the fully matured embryos, tracing their development and genes shows that they all arise from one common structure, even if heavily modified (M. Purdon).
 * Q: How do the similarities between the early development of fish embryos, reptilian embryos, and mammalian embryos support the idea of a common ancestor? (T. Russell)**

A: The similarities shared by these embryos supports the concept of a common ancestor, as these embryos have the same general corporeal pattern early in development, despite being rather unique from one another once they have developed beyond the embryonic stage. Each embryo consists of a head, body, and tail each of which look strikingly similar between classifications of animals. Note, how each embryo consists of a tail, despite whether or not the organism may have one once it is fully developed. This could be used to surmise that this is somewhat a vestigial structure for some organisms before it is dissolved during development (for those that do not have a tail) and a necessary structure for organisms that do have a tail once fully developed, either way, each is a remnant from their relation to an organism that had tailed-embryos because it had a tail itself, indicating a relation between them. (N. Braun)

A: The //Hox// gene is interesting in mammals because it is not only the 'organizer' responsible for the bodily makeup of flies, but can also be found in any animal with a body. This became evident when this gene found in mice provided evidence that it would have come from the duplication of the complement genes found in flies. The //Hox// gene can have an impact on evolution because it is what continues to link differing organisms together. Although these organisms have striking differences, they will still continue to rely on this gene for organization of the front-to-back and organ regions in order to continue to have reproductive success, resulting from the ability to use these physical characteristics to find mates and necessary means of survival. (O. Heltman)
 * Q: In Chapter 6, Shubin zooms in on the //Hox// gene. What is interesting about the //Hox// gene in mammals specifically? How can the //Hox// gene have an impact on evolution and why? (H. Schwarz)**


 * Q: Based on Shubin's description, what happens to an egg in the first three weeks after it is fertilized? Describe etopic implantation, and propose an explanation for how genes could play a role in how this problem is caused and how it could be solved. (P. Oakes) **

A: Although Sea anemones are very simple creatures compared to humans, they do indeed share specific traits of body plans with humans. Similar body axes seen between these two very different organisms tells us that they probably shared a common ancestor, and that every organism in between also shared that common ancestor. (L. Bercz)
 * Q: Sea anemones have a very primitive body plans compared to humans but they have similar axes compared to human what does this show about evolutionary similarity between the two? (C Hurst)**

A: By just looking at sea anemones and humans, they would appear to have almost no similarities. However, sea anemones have an oral-aboral axis, which is the predecessor of the human head-to-anus axis. Similar genes are active along both of these axes. And while sea anemones do not have the same belly-to-back axis as humans, they do have many active belly-to-back genes like humans. This all provides evidence that sea anemones and humans, no matter how different, must share some common ancestor. Sea anemones provide a simplified version of the body plan that makes all humans up and teach us even more about evolution. (C. Sanders)


 * Q: What caused the organs to be in the wrong place on the flies? (A. Gatje) **


 * Q: Shubin goes into great depth about the similarities and differences between humans and other types of organisms, including seemingly unrelated ones, in this chapter. How did he compare humans with jellyfish and their relatives? (N. Sarkar) **