Chapter+03

Place your questions and answers for Chapter 3 here.

A: The ZPA controls the formation of digits and toes in all animals. By increasing the size of the ZPA, and therefore increasing the number of cells in the ZPA and the concentration of the molecule the cells produce to form a pinky. With more of that molecule present, a larger distance would be required to make a thumb compared to a pinky based on the concentration and diffusion of the molecule since the absolute threshold to create a certain type of finger would be the same. (C.Nikolai)
 * Q: Based on the way the molecule made by the cells in the ZPA works, what procedure or variable might be able to increase the spread of the digits at the tip of a limb? In other words, what changes could you make that would encourage the digits to be farther apart/cover a greater distance? Why would this work? (A. Nolan)**

A: The //Sonic hedgehog// gene is one of many genes that help to create our limbs from shoulder to fingertip by turning on and off at the correct time. This gene could be mutated if there is something from preventing it from turning on properly (like a missing or extra nucleotide base). If this were to happen, and the gene didn't turn on during the proper time, then the animal would either have extra fingers (digits) or the pinky and thumb (opposite ended digits) would look similar. (J. terHorst) A: The hedgehog gene was first found in fruit flies as a gene that will create one region different from another. If there was a mutation in the signaling pathway then the molecules that instruct the cells to make different limbs and fingers wouldn't be able to do its job. Similarly this could lead to the creation of extra digits or digits looking exactly like one another. (A. Schmidt)
 * Q: What does the //Sonic hedgehog// gene do? How might this gene be mutated and what effect(s) do you think would occur as result if this gene were to be mutated? (T Gebhart)**

A: If every single piece of DNA were "turned on" in every part of the body all of the time then the cell would constantly be working and producing a lot of different proteins that it didn't need. There would be too much of everything and much of it would go unused. There would be no use for a skin cell to be producing the enzymes or proteins needed in the stomach, so anything that was produced would go to waste. The cell would eventually go into overload because of all of the processing and excess energy that it is spending on things it doesn't need. This whole mechanism evolved in order to save energy and to be more efficient. The cell doesn't have to waste energy or time creating something it doesn't need. It can put those things into use elsewhere and use them in a more valuable way. (L. Bentley)
 * Q: What do you think would happen if every piece of DNA were to be "turned on" in every part of the body all the time? Why did this mechanism of only "turning on" specific pieces of DNA for a particular type of cell evolve? (L. Bercz)**

A: The fact that the embryonic skates developed the EXACT SAME mirrored digit defect when exposed to the //Sonic hedgehog// gene from mice is evidence that similar genes are responsible for instruction on how to construct limbs across the animal kingdom. It showed scientists that the problem of fin-to-limb was not one of changing DNA, which narrowed the search drastically. The overarching idea is that there IS an inner fish after all. The difference between us and fish is smaller than people once thought. (P Oakes)
 * Q: What was the purpose of using mouse //Sonic Hedgehog// protein in skate embryo's and what information did it give scientists about the depth of the relationship between man and marine life? (C. King)**

A: This would cause the cells on the side of the new ZPA tissue to form digits and the side where the ZPA was previously to become malformed. This would hurt the chicken since its a waste of energy with no real gain. By moving the ZPA tissue to the other side, it has a mirror effect to the other side that it had previously. (H. Schwarz)
 * Q: A scientist moves the ZPA tissue to the other side of a chickens hand in the early stages of embryonic development. What would this cause and how could this be beneficial or also not to the chicken? (J. Speelman)**

A: Arthropods are invertebrates with an exoskeleton and segmented bodies. These segment of the body come in three major sections the head, Thorax and Abdomen. If the Hox gene is mutated there are many different ways the it could affect the arthropods. Crabs are arthropods that could be affected many ways by a mutated Hox gene. The mutated Hox gene could create a body plan of the crab with no pincers and instead and extra set of legs or it could do the opposite and get rid of a set of arms and instead add another set of pincers. (C. Hurst)
 * Q: One of the major ideas of this chapter is how the expression of certain genes, at certain parts of the body at certain times, causes the development of features within developing embryos. In this chapter, Shubin mainly focuses on the ZPA tissue, and the impact it has on lower limb development. Incorrect expression of genes, and therefore function of the tissue can lead to a number of defects during development. On the larger scale, a set of genes, called Hox genes, control the development of the body from the head to the tail. If Hox genes are expressed in the wrong location, they can result in body parts or organs growing in incorrect locations, such as the legs of a fruit fly growing where the antennae normally arise. How could mutations in Hox genes, especially in arthropods, result in new body plans? (M. Purdon)**

A: The hedgehog and sonic hedgehog genes in flies and chickens are responsible for making body segments different from each other. The patterns of activity Sonic Hedgehog specifically is comparable to the patterns from ZPA tissue. Due to the similarities between embryonic development in humans and chicken, I believe the Sonic Hedgehog gene in humans can be appropriately named as such. This gene is expressed in every limbed animal, including humans, to sculpt our limbs by timed expression; especially in our hands and fingers. The Sonic Hedgehog gene is an important sculpting factor that can be identified with the same name in any limbed animal, requiring no new name or classification due to its consistency in purpose. (M. Blanchard)
 * Q. Based on your knowledge of the role of the //Hendgehog// and //Sonic Hedgehog gene in flies and chickens... what do you think would be an a////ppropriate name for this gene in humans and why? (E. Olson)//**

A: This is relevant to finding our inner fish in the way that, in the ancient past, there were some genes that were turned on/off that ended up being advantageous to our fish ancestors. So, when these genes were kept in their beneficial settings, they aided in survival and reproduction. On an individual scale, organisms that have the gene set on its beneficial setting are more likely to survive and reproduce. On an evolutionary scale, individuals that are able to survive and reproduce are able to pass on their genes, so over time, the beneficial traits are passed on to subsequent generations. (T. Russell)
 * Q. Shubin often discusses that genes are constantly being turned on and off. Why is this so relevant when it comes to finding our inner fish? What does this mean for development on both an evolutionary scale and just for individual organisms? (C. Sanders)**

A: The connection between the //hedgehog// gene and ZPA is that they both seperate a what makes up a certain part of the body, making one region different from another. Thie //hedgehog// gene made one end of the flies body look different from the other end, which is similar to how ZPA made the chicken's pinkey finger different than the thumb. This correlates to finding this gene in other animals because it proves that the gene (or genes that have a similar effect) are found in animals as different as a chicken and a fruit fly, therefor it is highly plausable that similar genes are going to be found in animals such as chickens, mice, and fish. (E. Bach) A: The ZPA is the patch of tissue and overall region where the building process of hands are initiated while the hedgehog gene controls the differentiation of body regions in organisms and overall limb development. Although these processes are different, the sonic hedgehog gene is what bridges the gap. In chickens, the sonic hedgehog gene is active in the ZPA of embryo chickens, working with the ZPA in order to undergo normal limb development. When researching this process, scientists looked for the same ZPA and hedgehog gene in other organisms, in which they found in sharks, skates, chickens, and many more. Even when using embryo testing to splice one ZPA region onto another organisms embryo, animals were still able to develop normally, suggesting that these genes are very similar in many organisms. (I. Perler)
 * Q: What is the connection that Shubin makes between the function of the //hedgehog// gene and the function of ZPA? How does this correlate to their goal of finding this gene in other animals such as chickens, mice, and fish in order to find some proof that very similar genetic makeups can in fact be found in extremely differing** **organisms? (O. Heltman)**

A: The result of her experiment was that when she transplanted the patch of tissue, the limb developed normally except for that it also had a full duplicate set of digits that were a mirror image of the normal set. That patch of tissue must have contained crucial DNA that coded for the development of those digits. When the patch was moved, it was not altered in any way, which means that it carried out the process it was intended to. The specific genes coded for proteins that led to the development of new digits. (R. Heis)
 * Q: Some key experiments for understanding the devolopment of body part were experiments utilitizing chicken eggs. What was the result of Mary Gasseling's experiment where she took a patch of tissue from what would become a pinky side of the chicken's limb and transplanted it to the opposite side? From your knowledge on genes and DNA explain why you believe that this occured. (E. Bach)**

A: I think that this is very advantageous to an organism because it allows them to conserve energy and spend it elsewhere more important, increasing its chance of survival. Also, the different patterns of how genes are tuned on and off determine how cells act differently, for example a blood cell acts differently than a brain cell. With this ability, humans are able to use their cells to perform different functions. This is a major advantage to an organism, and is useful in adapting to a changing environment. (N. Sarkar) A: I think this is adventurous to organisms because having all of your cells running every single gene at once can be quite the energy consumer. So the fact that multi-cellular organisms are able to specify what each cell or group of cells does allows them to conserve this energy which could allow them to survive for longer, and this allows for specialization of cells within the multi-cellular organism which is highly advantageous. (T. McDaniel)
 * Q: Shubin talks a lot about how genes are only turned on in certain cells of the body at a time. So, if all cells have identical DNA but only some of the genes are turned on at a particular time, do you think this is advantageous to the organism in terms of survival and environmental adaptations? Why or why not? (M. McKinney)**

A: The patch of tissue that causes the pinky side to be different from the thumb side is called the zone of polarizing activity (ZPA). In regards to the development of chickens, it controls the number of digits they have. An anatomical point regarding life is the way that plants have the ability to absorb sunlight through their chlorophyll, and turn that into energy with water and carbon dioxide. Another fascinating thing about this is that these plants produce the oxygen we all need to survive as a waste product! (A. Gatje)
 * Q: According to the book, what is the "patch of tissue that causes the pinky side to be different from the thumb side" in regards to the development of chickens? Name one other anatomical or conceptual critical point as it regards to life, development or growth (plants might be a good thing to look at!), and explain how it is critical. (N. Braun)**