Describe the three types of selection: directional, stabilizing and disruptive and give an example of each in your own words.
Directional selection is a type of natural selection where it favors a single phenotype. It occurs in population when there is a shift towards an extreme version of the good trait. An example would be like creating new breeds of dogs over generations. For example, scientists who want dogs who can run fast will look for and select breeds who can run fast, and select the fastest runners from their offspring. Over time, after continuing the process they can produce a dog in a future generation who can run extremely fast.
Stabilizing selection is a type of selection where genetic diversity decreases as the population settles on a certain trait. Stabilizing selection favors the normal traits in a population. An example of stabilizing selection is choosing something in the middle, an average point. For example, animals must have certain traits to survive in an environment, so stabilizing selection chooses an average, normal trait for that animal so there are no extremes. The size of an animal would be an example, because in certain habitats, that animal cannot be too big or too small, so stabilizing selection chooses a medium size for that animal.
Disruptive selection is pretty similar to directional selection; it favors the extreme traits in a population. It is like the opposite of stabilizing selection. It is different from directional selection though, because sudden environmental changes cause sudden forces favoring a particular extreme. Disruptive selection occurs quickly. An example of this would be like the color of an animal. If a mouse had black fur and another had white fur, the offspring could have gray fur. However, the environment they are in may give an advantage to the black and white mice, therefore causing the mouse with gray fur to stand out. As a consequence of the selective environmental pressures the mice population would be disruptively selected for extreme values of the black and white mice, but not the gray mice.
Thursday, February 24, 2011
Wednesday, February 16, 2011
Blog # 3
Blog #3 Explain what micro evolution is. What are the three ways that variation occurs?
Micro evolution is a change in gene frequency within a population caused by mutations, natural and artificial selection, genetic drift and gene flow. Micro evolution is basically evolution resulting from genetic changes which may lead to new sub-species. An easier way to describe micro evolution is this: When someone with specific traits successfully reproduces, the next generation will have more copies of that certain trait; If the trend continues then that trait will become so common in a population causing the population profile (a chart which shows the number of people as a function of their ages) to change.
Firstly, genetic variation is the variety of genes in a population. The first and ultimate way that genetic variation can occur is through mutations. This is because mutations change the order of nucleotide bases of DNA. The second way that variation occurs is from independent assortment, which is the recombination of chromosomes during reproduction. Lastly, the third way in which variation happens is from crossing over during meiosis. Crossing over may result in the production or new combinations of genes.
Micro evolution is a change in gene frequency within a population caused by mutations, natural and artificial selection, genetic drift and gene flow. Micro evolution is basically evolution resulting from genetic changes which may lead to new sub-species. An easier way to describe micro evolution is this: When someone with specific traits successfully reproduces, the next generation will have more copies of that certain trait; If the trend continues then that trait will become so common in a population causing the population profile (a chart which shows the number of people as a function of their ages) to change.
Firstly, genetic variation is the variety of genes in a population. The first and ultimate way that genetic variation can occur is through mutations. This is because mutations change the order of nucleotide bases of DNA. The second way that variation occurs is from independent assortment, which is the recombination of chromosomes during reproduction. Lastly, the third way in which variation happens is from crossing over during meiosis. Crossing over may result in the production or new combinations of genes.
Blog #2
Why is fossil record hard to interpret?
The fossil record is basically a a collection or fossilized artifacts from all over the world. Many scientists hope to find more fossils to fill the missing "pieces" in the fossil record, which could help them greatly in discovering more of our past. However, this is difficult because only a very small fraction of the world's organisms have been fossilized, which makes it hard to study the fossil record. Organisms can only be fossilized in specific conditions, thus making fossilization very rare.
Furthermore, it is extremely challenging to interpret the fossil record, because often, the fossil can just be a blob that can not really be studied. Also, fossils from the same species are not guaranteed to survive equally well. Larger, lighter bones deteriorate quicker, while smaller more fragile bones are easily crushed, which makes it hard to even have a fossil to study at all. The different way the organism is preserved depends on the conditions it was in, therefore making it hard to interpret.
Sources:
http://www.wisegeek.com/what-is-the-fossil-record.htm
http://anthro.palomar.edu/time/time_1.htm
The fossil record is basically a a collection or fossilized artifacts from all over the world. Many scientists hope to find more fossils to fill the missing "pieces" in the fossil record, which could help them greatly in discovering more of our past. However, this is difficult because only a very small fraction of the world's organisms have been fossilized, which makes it hard to study the fossil record. Organisms can only be fossilized in specific conditions, thus making fossilization very rare.
Furthermore, it is extremely challenging to interpret the fossil record, because often, the fossil can just be a blob that can not really be studied. Also, fossils from the same species are not guaranteed to survive equally well. Larger, lighter bones deteriorate quicker, while smaller more fragile bones are easily crushed, which makes it hard to even have a fossil to study at all. The different way the organism is preserved depends on the conditions it was in, therefore making it hard to interpret.
Sources:
http://www.wisegeek.com/what-is-the-fossil-record.htm
http://anthro.palomar.edu/time/time_1.htm
Sunday, February 6, 2011
Sem. 2 Blog #1 Evolution
Why is evolution a theory and not a law?
Evolution is a theory because in order for it to become a law, it would have to be widely accepted and a supported, firmly held belief. Although evolution is supported by a lot of evidence, it isn't enough to make it into a law, which is unchangeable. Theories can be changed and tested and are beliefs that has been generally accepted from experiments and observations unlike laws, which are so firmly established that they often never change. Evolution cannot be a law, because some scientists don't agree with it and there has been much debate. For the theory of evolution to become a law, it must be accepted by all and have enough facts to go by.
Evolution is a theory because in order for it to become a law, it would have to be widely accepted and a supported, firmly held belief. Although evolution is supported by a lot of evidence, it isn't enough to make it into a law, which is unchangeable. Theories can be changed and tested and are beliefs that has been generally accepted from experiments and observations unlike laws, which are so firmly established that they often never change. Evolution cannot be a law, because some scientists don't agree with it and there has been much debate. For the theory of evolution to become a law, it must be accepted by all and have enough facts to go by.
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