Mackenzie+H.

January 24th, 2014 =Wiki Post #3= =Unit 3: Dynamic Equilibrium=

The Five Senses
====We often hear about "the five senses", though in reality humans possess more than five senses, the five main sense organs classified by Aristotle are extremely important to human life and can be said to include the "main" senses. The five senses, sight, smell, touch, taste and hearing help us interact with our environment and help set us apart from simple organisms.====

Sight
====The most developed sense in humans is sight. The organ for sight is the eyes, a tiny system of lenses and apparatus' that function a little bit like a high quality camera to project light on to the retina. The retina has many light-sensing cells that help analyze our world. Cone cells mostly pick up the color of things we see, while the rod mostly cells pick up the intensity of light, allowing our eyes to adjust to different levels of light. After being analyzed by the retina, visual information is sent down the optic nerve to different parts of the brain, but the main part of the brain associated with sight is the visual cortex in the back of the brain.====



Hearing
====Close behind sight is our second most developed sense, our hearing. The shape of our ears help direct incoming sound waves into the ear and the reason we have two is to be able to tell which direction the sound is coming from and from how far away it is. Once inside, they interact with the tympanic membrane, or eardrum, a cone shaped membrane that amplifies sound and sends it to the ossicles in the middle ear, three very small bones who transmit the vibrations received from the eardrum to across the bone structure and into the cochlea. The cochlea is a spiral shaped cavity filled with fluid and lined with nerve fibers that we usually call the hairs in our inner ear. The movement of these nerve fibers will create an impulse that will be sent through the nervous system to the brain where it is processed by the auditory cortex, which are small sections in the middle on either sides of the brain.====



Smell
====Our sense of smell, or the olfactory response, may not be as strong as some other animals, but it is important to us nonetheless. What we smell are really just vapors given off by whatever we are smelling. They are in fact tiny little pieces of that substance. These vapors enter our nose and their molecules interact with the cilia attached to the olfactory bulb that sends a nerve impulse to the brain which interprets it as a specific smell.====



Taste
====Closely linked with smell, the sensation of taste uses our tongue, and other parts of our mouth, to sense the flavor of whatever is in our mouth. Saliva breaks down whatever we are eating and chemicals from the food bind to taste cell receptors in the taste buds in our mouth. These send a nerve impulse to our brain which will interpret it as a certain taste. It is thought that different areas of our tongue generally taste different tastes better, be it salty, sweet, bitter, sour or umami, but this has been disputed. Our sense of taste is thought to have evolved to encourage us to eat the right things we need to eat, such as salts and carbohydrates and encourage us not to eat poisonous things, which are often bitter or sour.====



Touch
====The sense of touch starts in the nerve endings in the peripheral nervous system distributed all over our body. When we touch something, the nerve endings fire the nerve impulse to our brain. The neurons will fire faster or slower depending on how much force is being directed at the nerve endings. Using touch, we can identify contact with something, the temperature of things around us and feelings of pain, all depending on how neurons fire. Interestingly, the hairs on our skin help stimulate our sense of touch before we actually touch something and different parts of our body have a higher or lower concentration of nerve endings.====

====These five senses all work together to help us experience life to its fullest extent, yet as they work together the five senses can help us experience senses different from what they can do individually. There are also other senses, such as our sense of balance, which help us as well. Here is a video explaining more about how the five basic senses work together with the nervous system to help the body.==== media type="youtube" key="GnqKkPGV7JE" width="504" height="283" align="center"

Interesting Related Websites For Further Reading
Some information on what our other senses are: http://science.howstuffworks.com/life/question242.htm More about umami, the fifth taste: http://www.msginfo.com/about_taste_umami.asp Interesting information about Synesthesia, the jumbling of senses: http://www.livescience.com/169-rare-real-people-feel-taste-hear-color.html Information on taste disorders: http://www.nidcd.nih.gov/health/smelltaste/pages/taste.aspx

What is it?
====When we talk about evolution, we are usually referring to things evolving from one species into a whole other species. For example, the evolution of dinosaurs into our current birds. Micro evolution is small scale evolution or evolution within a population. It is defined as "a change in allele frequency in a population". For example, a virus could evolve to be resistant to certain treatments. It's still the same virus, yet there was a change in it's genes that it will "pass on".====

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 * Small Sample Size:** Small sample size can easily change the allele frequency in a population. For example, if you have a 50% chance of grabbing either a red or green marble from a jar of 100 000 marbles and you repeat this 1000 times, you should get approximately 50% red and 50% green. It will become more and more close to 50% as your sample size approaches the maximum. But if you only take out ten marbles, you could end up with 8 green and 2 red or even 10 red and 0 green. The same thing happens with mating. There is a much higher rate of fluctuation in allele frequency in smaller population samples.=====

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 * Non-random mating:** Obviously if mates are being chosen based on a particular trait they have eventually the population will change so that more and more members have that trait. This is one of the things that pushes micro evolution. Micro evolution is shown really well when we look at examples of inbreeding in humans of the past (such as royalty) or pedigree dog breeding of the present. In each example, we breed together members of the population with similar traits to produce offspring with those traits, eventually driving the gene pool in that direction.=====

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 * Mutations:** If an organism in a population mutates and has children that have this mutation, this will change the allele frequency in the population. Though a few mutated organisms in a population of 1000 or so won't really make too much of a difference. It is when mutations are paired with any of the other four causes that they make a difference.=====

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 * Gene flow:** Also called migration, this is when organisms from another population join the population we are looking at (immigration) or organisms from the population we are studying leave it (emigration). If we have 4 yellow labs and 4 black labs in our population then we have 3 yellow labs emigrate in, then the allele frequency will change.=====


 * Natural Selection:** The tendency for nature to play a part in which genes get passed on to the next generation. This is basically the strongest survive type of idea. Nature either selects for or against certain traits. For example, a bacterial colony is infecting somewhere in your body. You treat it with antibiotics. The bacteria who are not resistant to it die off, while the ones who are survive and keep breeding. We then end up with a large population of those who are resistant to the antibiotic and those who are not are mostly gone.

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Here is a video that talks about the five things <span style="background-color: transparent !important; background-position: initial initial !important; background-repeat: initial initial !important; border: none !important; display: inline !important; float: none !important; font-family: arial,helvetica,sans-serif !important; font-size: 13px !important; font-style: normal !important; font-variant: normal !important; font-weight: normal !important; height: auto !important; line-height: 19px !important; margin: 0px !important; min-height: 0px !important; min-width: 0px !important; padding: 0px !important; text-decoration: underline !important; vertical-align: baseline !important; width: auto !important;"> micro evolution.

What's next?
As a population continues to evolve in this manner, it could experience speciation, the process in which they split into different species. A species is defined as a group of organisms that can freely breed together in nature, so speciation would be when the groups with different traits in a species can no longer breed together. An example of this speciation would be wolves with the right genes to be able to be domesticated splitting of from the rest of the pack and eventually become the first dogs. We can consider this macro evolution. So enough micro evolutions can end up becoming a macro evolution as they are essentially the same process but over different time periods.

Interesting Related Websites For Further Reading
More about the origin of the first birds: [] More on population genetics including gene flow: [] A bit about Darwin's research on the Galapagos islands leading to his theory of evolution: [] An article on the negative sides of inbreeding: []

Genes and Inheritance
====As living things, we humans are a product of our genes and our environment. The environment encompasses things like our upbringing, social, climate and so on. Our genes are essentially what links us to our parents, their parents and the rest of our family. We inherit our genes from our mother and father and they inherited their genes from their mother and father. Genes are sequences of base pairs on our DNA which is coiled up into chromosomes in the nucleus of our cells. Our genes code for certain proteins to be made when they are read during the transcription process after translation, these proteins determine things like height, eye color, hair color and what genetic disorders you are predisposed to getting.====

====Our DNA can change for different reasons and this can either be helpful, like the chameleon's ability to blend in with it's environment or harmful. Genetic disorders are caused by mutations in one's DNA that proves to be harmful. There are 4 different categories of genetic disorders: single gene disorders, a mutation in a single gene; chromosome abnormalities, problems with whole, or parts of, chromosomes; multifactorial disorders, a combination of mutations in several genes and sometimes environmental factors; and mitochondrial disorders. Because we inherit our parents' DNA and through that, their genes, it is possible that they may pass on genetic disorders to their children.====

media type="youtube" key="K3F5BV82Lg8" width="560" height="315" align="center"

Here is an interesting video that explains a little bit about genes and inheritance. On top of talking a bit about inheritance, it also explains how genes were discovered, which is quite interesting.

Passing on Genetic Disorders
====There are two types of genes; dominant genes and recessive genes. Dominant genes always win over one recessive gene. Following this logic there are two types of mutated genes in autosomal chromosomes (non-sex chromosomes) which can cause a disorder. There are dominant gene disorders and recessive gene disorders. Of the two copies of chromosomes in each parent, only one is passed on to the child. So it is possible that one chromosome has the gene with the disorder and the other does not. In a recessive gene disorder, the child needs to receive a gene with the disorder from his mother and from his father. If only one of them passes it on, he will only have one copy of the gene and will not have the disorder. He will, however be known as a carrier. This means he can pass the gene on to his children. In a dominant gene disorder, only one of the chromosomes needs to have the gene with a disorder on it for it to really give the person this disorder. So if a person has a dominant gene disorder passes on his chromosome with the dominant gene disorder on it to his child, his child will have the disorder as well, but if a person passes on his chromosome with a recessive gene disorder to his child and the wife does not, the child will not have the disorder, but will be a carrier.====

Here are some images to illustrate this:




Factors That Cause Chromosomes to Mutate
====Other than inheriting a problem that is already apparent in your parents genes, it is possible to get a genetic disorder due to a problem just with the sex cells or with the growth of a fetus. Here are a few examples of this:====

**-Problems during Meiosis:**
====In humans meiosis begins with one cell with 46 chromosomes that divides into 2 cells with 46 chromosomes through a process slightly similar to mitosis, except with the crossing over of chromosomes into tetrads where they exchange genes, then another division without copying the chromosomes again. This results in 4 unique haploid daughter cells (23 chromosomes each). If there is an error with this process, it could result in an incorrect number of chromosomes in the sex cell which could then result in a fetus developing with an incorrect number, or damaged, chromosomes in the nucleus.====



**-Problems During Mitosis**
====After the egg is fertilized and the cells begin to go through mitosis, similar errors can occur during this process like the ones in the making of gametes. Meaning the chromosomes can also not copy correctly in this stage. Errors like this can result in a problem called mosaicism. Mosaicism is when chromosomes in some cells divide differently than those in others so it results in many cells having different amounts of chromosomes.====



**-Age of parents**
====Because the mother is born with all of her eggs, it can be said that the eggs grow old with the mother. There is evidence to suggest that problems with the chromosomes in the eggs can occur over time. That being said it is best to have kids at a younger age, to a certain extent. James Watson, of the famous Watson and Crick, recently estimated that the ideal time to have children would be around 15 years old. Now, this is not really a good moral solution, so he advises that we get DNA from males at age 15 and have births by in vitro fertilization. The mother should not be much past 30 in the case and definitely not 40, ideally. Interestingly, in the past people believed that the age of the father did not matter and it was only the "fault" of the mothers age if something happened to the baby during the fetus growth period. New evidence suggests it is also affected by the age of the father as well.====

Interesting Related Websites For Further Reading
More information on Mitotic nondisjunction: [] Information about family relations: [] More information on how age affects female sex cells: [] Information on environmental factors that can harm DNA: []