16.2+Evolution+as+Genetic+Change_6th

 **__Mark and Danny's Super Amazing Awesome Wiki on Natural Selection on Single Gene Traits and Polygenic Gene Traits!__** media type="custom" key="3461102" (MP/DS)  (MP)
 * 1) Natural Selection on a Single Gene Traits.
 * 2) Natural Selection on single-gene traits can lead to changes in allele frequencies and thus to evolution. (MP)
 * 3) An example of natural selection on a single gene trait is the lab we did on Tuesday. The single trait for the moths was color and size. The largest moths and the white moths were the ones that stood out most to the prey so these moths would be the least likely to reproduce and pass on their genes. (MP)
 * 4) EXTRA FACT!: If an allele does not have an effect on an organim's fitness then it will not be put under pressure. (MP)
 * 5) Natural Selection on Polygenic Traits
 * 6) Natural selection on polygenic traits is more complex than on single gene traits. (DS)
 * 7) Three ways that natural selction can affect the distribution of phenotypes are directional selection, stabilizing selection, or disruptive selection. (DS)
 * 8) Directional Selection (First Mode) (DS)
 * 9) This occurs when the allele frequency of a trait shifts towards one extreme on the graph. This means that one phenotype is the best trait for higher fitness. Since that trait is needed more to survive, the other variations become less common because the organisms with that trait have a worse chance to survive and pass on their genes to offspring. A simple example of directional selection is the beaks of finches. Say there are three finches in a habitat. One finch's beak is built for large seeds, another's medium sized seeds, and another's small seeds. If large and medium sized seeds become scarce then the finch with the beak for small seeds has the highest fitness of the three, and therefore is more likely to pass its genes on to offspring. (DS)[[image:http://trc.ucdavis.edu/biosci10v/bis10v/week6/directional.gif width="720" height="540" caption="Directional Selection with Peppered Moths" link="http://trc.ucdavis.edu/biosci10v/bis10v/week6/directional.gif"]](MP)
 * 10) Stabilizing Selection (Second Mode)
 * 11) This is when the individuals near the center of the bell have higher fitness than the two other extremes. In simpler terms this is when the average/normal organism has a higher fitness than the other variations. An example of stabilizing selection is human birth. If you are too small when you are born your risk of infant death is very high. If you are too large you risk not being born at all. So, for babies the safest size is the happy medium. (MP)
 * 12) Disruptive Selection
 * 13) <span style="font-size: 90%; font-family: 'Comic Sans MS', cursive;">This is when the two extremes are the individuals with the highest fitness and the average has the lowest fitness. An effect of disruptive distribution is it creates two distinct phenotypes and rarely any average between the two. An example of disruptive selction is shown in an experiment conducted by two scientists Thoday and Gibson. They used fruit flies to show an example of disrputive selection. They had three groups of fruit flies with high, low, and medium numbers of bristles on their body. The fruit flies with a medium number of bristles were prevented from breeding, and after a few generations the amount of fruitflies with a medium number of bristles decreased significantly. See graph below. (MP/DS).[[image:http://www.blackwellpublishing.com/ridley/images/disruptive_selection.jpg caption="Disruptive Selection using fruit flies" link="http://www.blackwellpublishing.com/ridley/a-z/Disruptive_selection.asp"]](MP/DS)
 * 14) <span style="font-size: 90%; font-family: 'Comic Sans MS', cursive;">Genetic Drift
 * 15) <span style="font-size: 90%; font-family: 'Comic Sans MS', cursive;">Simply by chance different organisms with different alleles can end up in different places. This random shifting of alleles is referred to as genetic drift. (MP)
 * 16) <span style="font-size: 90%; font-family: 'Comic Sans MS', cursive;">Genetic Drift works like this: In small populations, individuals that carry a particular allele may have more descendants than other individuals, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population. An example of when genetic drift may occur when a small group of individuals finds a new habitat. These individuals may have a more specific or more random allele frequencies than the rest of the habitat they came from. (MP) [[image:http://biology.unm.edu/ccouncil/Biology_203/Images/PopGen/bottleneck.gif caption="Genetic Drift" link="http://http//biology.unm.edu/ccouncil/Biology_203/Images/PopGen/bottleneck.gif"]](DS)
 * 17) <span style="font-size: 90%; font-family: 'Comic Sans MS', cursive;">Founder Effect
 * 18) <span style="font-size: 90%; font-family: 'Comic Sans MS', cursive;">Is known as a situation in which allele frequencies change as a result of the migration of a small subgroup of a population. An example is fruit flies found on different Hawaiian Islands. They all descended from the same species but due to their change in habitat their allele frequencies have changed as well. (MP)
 * 1) Hardy-Weinberg Equilibrium (DS Whole Section)
 * 2) The Hardy-Weinberg equilibrium is a principle that allele frequency will stay constant overtime if it is not affect or changed by any forces. There are five forces that would have to happen to create a constant allele frequency. They are:
 * 3) Random mating- There is no preference in mating. A male with one trait does not prefer a female with another trait.
 * 4) Large population- A large population is not changed as much by a rare or uncommon phenotype than a small population would be.
 * 5) No mutation- Alleles cannot change or variations will occur.
 * 6) No migration- No genes must be shared with other populations. No new genes can be brought into the population.
 * 7) No natural selection- Natural selection cannot favor individuals with a certain gene.

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