Chapter+08

Place your questions and answers for Chapter 8 here. Due to their mammalian history, the smelling genes that dolphins have are unlike those of other aquatic creatures (fish), because they do not code for a water-specialized method of smelling (they are air-specialized), essentially making them useless (along with the development of their blowhole, which they use to breath instead) in an aquatic environment and subject to mutations that are able to pass on generation to generation due to the fact that they are manipulating archaic genetic information. In short, there is no reason for a nasal passage because they are unable to smell underwater and have developed blowhole in order to breathe. As mentioned before, there really is no reason for these genes to remain, hence why they are able to be mutated and continue to be passed on to future generations. (N. Braun)
 * Q: Some animals, such as dolphins and whales, have all the normal smelling genes but no nasal passage to smell, why might this be and is there any reason for the genes to remain? (I. Perler)**

A: These 300 odor genes have been knocked out because they are no longer needed anymore. In earlier times, our ancestors relied a lot more on their sense of smell. Nowadays, we rely on our vision more than we rely on our sense of smell. This is a beneficial change. Why have certain genes turned on that we don't even utilize? It would be a complete waste of energy for these genes to be functioning and not even use them. It's also beneficial in terms of being able to evolve with our changing environment--such as relying on our sight more. (T Gebhart).
 * Q: Shubin explains that 3% of our genome is devoted to odor genes, but at least 300 of these genes, in humans, do not function due to mutations. What is the reason for why these genes have been "knocked out," and describe why you think this was a beneficial change or not. (J. terHorst)**

This makes sense because mammals are more evolved, so there has been more time evolutionarily speaking for the primitive odor genes to be copied and mutated slightly over time, where the beneficial ones remained and were passed on from generation to generation. As fish evolved to amphibians, to reptiles, and eventually mammals, this sense of smell was used more and more because it was beneficial in tracking prey for food. Because a heightened sense of smell would be so beneficial to an animal, any mutated odor gene that allowed for a new smell to be sensed would be beneficial, and thus passed on to generations, resulting in mammals having a much higher number of odor genes after a significant amount of time (A. Nolan).
 * Q: Mammals have a much higher number of oder genes when being compared to jawless fish. Why does this make sense? (A. Schmidt)**

A: The process is sort of like a lock and key sort of example. When you or something smells, odor molecules go up into the nasal cavities which get stuck in mucus and interact with nerve receptor for the never cells. The nerve is then sent up to the brain where the odor is decided. It is advantageous for a strong sense of smell for stuff like tracking or for escaping from danger. For example, if there is a fire, it produces a distinct smell and can help you to get out of there asap. Dog's sense of smell is better than the sense of humans because dogs have more olfactory receptors by 50x (humans - 6 million; dogs - 300 million). (J. Speelman)
 * Q: What is the process as our brain receives and responds to a smell? How is it advantageous for humans to have such strong senses of smell - how does this compare to an animal like a dog, whose sense is even stronger? Why? (M. Blanchard)**

A: Axel and Buck's three correct assumptions were about what the odor receptors may have looked like, what specific activities the genes for these receptors had, and that there were a very large number of olfactory genes. Axel and Buck could have come up with these assumptions through investigating work done through other laboratories, investigating straight forward ideas like the one pertaining to gene activity and how it should only be involved in smelling, and through the use of the everyday idea where one thing can stimulate a specific smell completely different from another thing. Evidence that could have been used to support their ideas could have been found primarily in the genome and the structure of the olfactory genes to prove their hypotheses. (O. Heltman)
 * Q: What were Axel and Buck's three correct assumptions? How do you think they came up with these and what possible evidence did they use? (C. Nikolai).**


 * Q: Think about what Yoav Gilad discovered in primates about smell and sight. Does this discovery help support that fact that 3% of genes are odor genes in humans? Why or why not? (L. Bentley)**

A: In cetaceans, or modern whales, the nasal passageway is modified to exit at the top of the head, allowing the individual to breath without fully extending their head above the water. Along with this change, almost all of the genes for odor have been 'knocked out', rendering them unable to function. This is because the odor genes are tailored for scents in the air, not in the water. This means that the genes carried over from their land breathing ancestors would be functionally useless to modern aquatic cetaceans, therefore rendering any mutation knocking the genes out neutral. (M. Purdon)
 * Q: Describe the transformation of nasal passageways in organisms like dolphins and whales. What are they used for? What are the gene's role? Why is this development advantageous for these types of organisms? (R. Heis)**

Jawless fish, such as lampreys and hagfish. These are the most primitive fish alive on the planet today. (A. Gatje)
 * Q: Which class of animals could have a need for both air-based nasal neurons and water-based nasal neurons, not just one or the other? (T. Russell)**

A: The extra odor genes all look to be variations of the genes seen in jawless fish. The genes seen in primitive species like the jawless fish are almost copies of the extra odor genes we have today, amidst the vast number we have of odor genes today due to mass duplication. This origin allows for the creation of more odor genes very fast and efficiently if they prove to be advantageous. However, as we see, most of these extra odor genes are rather useless as we turn to sight or sound more rather than smell in our society. (M.McKinney)
 * Q: Where do extra odor genes come from? Why do they have the specific origin that they have? (H. Schwarz)**

It would be beneficial to have only one type of receptor (for water or air) if the organism lives strictly in water or on land -- this could aid the organism in survival, as only one type of scent receptor can cause it to be more powerful than if there were two for both air and water, if they don't need the other type for survival. At this point, it would just be a waste of space and energy for it to have both receptors. However, it would be very beneficial for half land half aquatic animals to have smell receptors for both water and land so that they are able to receive and process scents in both environments to increase their fitness. (L.Bercz)
 * Q: In this chapter we learn there are receptors made for receiving smell in water and receptors made for receiving in the air. Why would it be beneficial to have one type of receptor and why would it be beneficial to have both? (C. Hurst)**


 * Q: How could you extract the DNA from a turnip in the comfort of your kitchen? How will this state compare to the what we learned about the organization of DNA in our study of mitosis and meiosis? (P. Oakes)**

A. It functions like a lock and key, the lock being the odor molecule and the key being the receptor on the nerve cell. the odor molecules are sucked into the nostril and the get stuck to the to mucous in the nasal passage. nerve cells stick up into the mucous lining and when they bond to an odor molecule they send signals to the brain which are then recorded as a smell. each nerve receptor is specific to a certain odor, so some molecules might send lots of signals to the brain, while some may not. (E.Olson)
 * Q: How does our sense of smell work? (A. Gatje)**

A: In today's world, humans need to be able to see what's going on around them rather than just smelling it. In the past, perhaps living in a less modern world, people needed to be able to smell the environment around them. Animals use smell to hunt, and also to recognize others. However, humans now recognize one another by sight. We need to be able to see so that we can safely navigate our environments. If we couldn't see the way we can, driving would be totally unsafe and smell wouldn't really offer much help behind the wheel. (C. Sanders)
 * Q: Shubin explains how "humans are part of a lineage that has traded smell for sight." Why do you think that in the past there has been more of a reliance on smell rather than sight, and that now there is more importance in sight rather than smell? (N. Sarkar)**

A: Smell enhances our other senses, allows us to sense predators and danger, as well as things we like. It also aids in memory when certain smells trigger the brain. These things are all evolutionarily beneficial because it allows us to pass our ability to smell onto our offspring, giving them a better chance of survival. **(**A. Gatje)
 * Q: What makes smell so beneficial that 3% of the human genome is dedicated to just detecting odors? How is this evolutionary beneficial?(T. McDaniel)**