Totaled 3/29 Mr F

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Totaled 3/20/10 Mr F

 

Microevolution is the occurrence of small-scale changes in allelle frequencies in a population, over a few generations, also known as "change below the species level"

                  - Describing Genetic Structure- genotype and allele frequencies

For Example: You have a bunch of frogs where G= green and g= brown.

Frogs	Genotype Frequencies	Phenotype Frequencies	Allele Frequencies
100GG 160Gg 140gg     Total Frogs: 400   Total # of alleles: 800	100/400= .24GG 160/400= .46Gg 140/400= .35gg	260/400= .65 green 140/400= .35 brown	360/800= .45G 440/800= .55g

How to do the above calculations/H-W & more:

p^2 = BB, homo dominant

q^2 = bb, homo recessive

2pq = Bb, hetero dominant

 

How to Solve The Equation

The main point of the H-W equation is to determine the number of organisms in a population that are AA, Aa, and aa for a gene, given that you have a sample population. Follow these steps to be successful at using the H-W equation.

1. Determine the proportion of individuals that are homozygous recessive (aa) by dividing the number that exhibit the recessive trait by the number that is sampled. This number is q^{2 (you will most likely be given q^2 in some sort of data form, etc.)}

2. Take the square root of this number to determine q

3. To find p, subtract q from 1. Remember p + q = 1.

4. Now that you know both p and q (the allele frequencies) you can determine the number of individuals that are homozygous dominant: p^{2 (Remember this number is a proportion, so the problem may call for you to state actual number of individuals in your population. Multiply this number by your total population)}

5. You can also determine the proportion of individuals that are heterozygous by this part of the equation: 2pq = the number of heterozygous individuals.

6. Check your work by making sure that your numbers all add to 1.0.

(http://www.biologycorner.com/bio4/notes/hardy_weinberg.php)

 

Adding on to the satement above, these changes may be due to several processes: mutation, natural selection, artificial selection, gene flow and genetic drift.

 

Mutations are changes in the DNA sequence of a cell's genome and are caused by radiation, viruses, transposons and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication. Mutations also create new alleles and ar the untimate source of all genetic variation.

This video is helpful in showing the causes of genetic mutations  

Natural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations. It is a key mechanism of evolution because it leads to adaptation.

 

Artificial selection (or selective breeding) describes intentional breeding for certain traits, or combination of traits.

 

Microevolution can be contrasted with macroevolution, which is the occurrence of large-scale changes in gene frequencies in a population over a geological time period (i.e. consisting of extended microevolution). The difference is largely one of approach. Microevolution is reductionist, but macroevolution is holistic. Each approach offers different insights into the evolution process.

 

In population genetics, gene flow (also known as gene migration) is the transfer of alleles of genes from one population to another.

 

Genetic drift or allelic drift is the change in the relative frequency in which a gene variant (allele) occurs in a population due to random sampling and chance: The alleles in offspring are a random sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces. A population's allele frequency is the fraction of the gene copies that share a particular form.

 

This video does a great job of explaining the differences between micro and macroevolution. Also, it explains how one could not exist without the other, for macroevolution is just a build up of lots and lots of microevolution.

 

This not actually an example of micro evolution but rather a popular depiction of the evolution of "man". This gives the false impression that our distant relatives were apes & chimps, which is not true. Place these on a clade and they point to a common ancestor in the past - which is not the same thing. Mr F

 

This age-old graphic still makes for a perfect example of how microevolution occurs over long periods of time with many small schanges along the way.

 

Here is an interesting web quest type thing about microevolution - http://evolution.berkeley.edu/evosite/evo101/IVMicroevolution.shtml

 

Microevolution is the occurrence of small-scale changes in allele frequencies in a population, over a few generations, also known as "change below the species level"

 

Macroevolution is a scale of analysis of evolution in separated gene pools Macroevolutionary studies focus on change that occurs at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population

 

Microevolution is simply a change in gene frequency within a population. Evolution at this scale can be observed over short periods of time — for example, between one generation and the next, the frequency of a gene for pesticide resistance in a population of crop pests increases. Such a change might come about because natural selection favored the gene, because the population received new immigrants carrying the gene, because some nonresistant genes mutated to the resistant version, or because of random genetic drift from one generation to the next.

 

 

Mutations  Notes on the follwing paragraph. This is the type of simplifed thinking that is put forth by those who do not understand what and how evolution works.

Mutations are caused by random changes in genes. Is it possible that a mutation could produce new genes that would create a new species? Yes it possibly could but first it only increases the variation within a species. Natural selection (selection pressure) takes it from there. Let's consider that possibility.

It is possible that somewhere there could be a colony of flying ants. It might happen that the queen of this colony might suffer some genetic accident that damages the gene that causes wings to form. Her offspring would not have any wings, and naturally would not be able to fly ok variation. .

The inability to fly is certainly not an advantage (If they find a niche they can exploit it was advantagous if not oh well), so one would not expect that natural selection would cause them to beat the flying ants in the battle for survival likely they would not be competing for the same resources anymore. This mutation would be a disadvantage. But inability to fly might not be such a large disadvantage that the non-flying ants could not survive. (again, depending on conditions. Is the phenotype "fit"?) These non-flying ants might not mate with the flying ants, and so they would be considered to be a new species. This is not evolution in the Darwinian sense because a "higher" (or superior) species has not been created (who ever said that it had to be more complicated or "superior"?. Quite the opposite. This hypothetical new species of ant is a step backwards, not forwards. (evolution does not move "backwards" it constantly tests phenotypes for fittness (reproductive fitness) only. If the traits you have work you're good, if they don't, oh well.  It has lost the ability to fly because it has lost a required gene. It now also has some left-over "junk DNA" designed to control the wings it no longer has. This junk DNA no longer serves any purpose. As you should know by now, there are lots of "junk DNA sequences in our DNA that probably are "partial something or others that we don't use anymore (appendix anyone?)

It could be said that the ant "devolved" (OK now this is pissing me off. Strictly speaking time flows one way and so does evolution. Who ever said that complexity is better?)because the new species is inferior (aarrgghh,  If it is adapted to its resources it is fit and will survive. Inferior? why? Are cave salamanders inferior to forest salamanders because they lost the ability to see? put a "sighted" salamander in a cave and see who has the advantage). Devolution is consistent with the second law of thermodynamics. Given enough time, and left to themselves, things fall apart. Things don't naturally fall together. So it is possible that flying ants could devolve into ordinary ants because one of the genes needed for flying could be lost or damaged.  1st there is no such thing as de-evolution. Do not equate thermodynamics with evolution

For flight-challenged ants to evolve into flying ants, at least one new gene would have to be added. There is no evidence that this happens now, or has ever happened in the past. Oh yes there is!!!! "Gene-jockey" scientists have transplanted genes to create novel characteristics in laboratory animals, but new beneficial genes don't just appear by magic in a natural process. (that whole mutation thing seems to elude this guy) Genes naturally get worse, not better.

If you write a document, then let someone change some of the letters at random, the document will make less sense, not more sense. If you randomly change op codes in a computer program, the program will not improve. Random mutations do not make things better. Ahhh... but they do. just very infrequently so it requires a very long time.

You must read this stuff with a critical eye!

The above diagram is again a simplification of the process and incorrect.

 

16.2 Evolution as Genetic Change

 

 

·         Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution

·         Natural selection can affect the distributions of phenotypes in any of three ways: directional selection, stabilizing selection, or disruptive selection

·         In small populations, individuals that carry a particular allele may leave 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

·         Five conditions are required to maintain genetic equilibrium from generation to generation: There must be random mating; the population must be very large; and there can be no movement into or out of the population, no mutations, and no natural selection.

 

 

·         directional selection- form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

·         stabilizing selection- form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end

·         disruptive selection- form of natural selection in  which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

·         genetic drift- random change in allele frequencies that occurs in small populations

·         founder effect- change in allele frequencies as a result of the migration of a small subgroup of a population

·         Hardy-Weinberg principle- principle that allele frequencies in a population will remain constant unless one or more factors cause the frequencies to change

 

 

---This podcast explains microevolution and the Hardy-Weinberg equation in depth. The man shows graphs and how evolution relates to genetics.

 

·         genetic equilibrium- situation in which allele frequencies remain constant

 

This video is great- it is slow and really easy to understand.  It gives examples that are easy to understand.

 

http://www.newworldencyclopedia.org/entry/Microevolution---> This link is very helpful in understanding the basic principals of Microevolution.

 

 

Microevolution vs. Macroevolution

 

Traditionally, microevolution is defined as evolution within a species. That is microevolution involves small changes that do not create new species. On the other hand, macroevolution creates new species. With these definitions, the pictures across the top and down the right side of this page are both examples of macroevolution. This web site will show that while the variation across the top can be explained by natural selection, genetic drift and mutations the variation down the side cannot. In light of this observation, a better definition for microevolution and macroevolution is required. This web site will use the following definitions:

Microevolution are changes in the gene pool that do not create new genes. That is every gene in the new gene pool has a similar function and purpose in the original gene pool. A gene that is altered by mutations, but maintains its original function and purpose is called an allele. Alleles are different variations of the same gene. Microevolution creates new alleles. It does not create new genes. Macroevolution: changes in the gene pool that create new genes. Since new organs and structures require new genes, any evolutionary transition that involves a new structure or organ is an example of macroevolution.

The variation in the large cats across the top does not require new genes. Therefore, this variation is an example of microevolution. Traditional Darwinian principles can explain this variation. On the other hand, the variation down the right side requires new genes. This variation is an example of macroevolution. This web site will show that genetic drift and natural selection operating on the variation created by mutations cannot create new genes. Thus, the theory of evolution cannot explain the origin of new organs and structures, and evolution does not explain the origin of complexity.

Why is the distinction between microevolution and macroevolution so important?

 

Experiments designed to test evolution always test microevolution. If macroevolution is possible it is too slow to be observed. So while the experimental evidence supporting microevolution is undeniable, the same cannot be said for macroevolution.

Scientists have theorised that given enough time microevolution can explain macroevolution. The logic behind this extrapolation rests on the traditional definitions for macroevolution and microevolution. New genes are not required for macroevolution as long as such evolution is limited to closely related species (for example - tigers and lions). In this example, the processes behind microevolution and macroevolution are identical and extending microevolution to explain macroevolution makes perfect sense.

On the other hand, this extrapolation is very hard to justify when microevolution is extended to explain the origin of new organs or structures. Since the evolution of new organs and structures requires new genes, microevolution can only be extended to explain macroevolution if the processes responsible for new alleles can also create new genes. Creating a new gene with a new function is clearly different than optimising a gene without changing its function (creating a new allele). So the first and foremost question at hand is can the processes that create new alleles also create new genes? Existing genes are not free to evolve into new genes.

 

There is one particular aspect of evolution that needs to be given specific attention: the somewhat artificial distinction between what is called “microevolution” and “macroevolution”, two terms often used by creationists in their attempts to critique evolution and evolutionary theory.

Microevolution is used to refer to changes in the gene pool of a population over time which result in relatively small changes to the organisms in the population — changes which would not result in the newer organisms being considered as different species. Examples of such microevolutionary changes would include a change in a species’ coloring or size.

Macroevolution, in contrast, is used to refer to changes in organisms which are significant enough that, over time, the newer organisms would be considered an entirely new species. In other words, the new organisms would be unable to mate with their ancestors, assuming we were able to bring them together.

You can frequently hear creationists argue they accept microevolution but not macroevolution — one common way to put it is to say that dogs may change to become bigger or smaller, but they never become cats. Therefore, microevolution may occur within the dog species, but macroevolution never will.

There are a few problems with these terms, especially in the manner that creationists use them. The first is quite simply that when scientists do use the terms microevolution and macroevolution, they don’t use them in the same way as creationists. The terms were first used in 1927 by the Russian entomologist Iurii Filipchenko in his book on evolution Variabilität und Variation. However, they remain in relatively limited use today. You can find them in some texts, including biology texts, but in general most biologists simply don’t pay attention to them.

Why? Because for biologists, there is no relevant difference between microevolution and macroevolution. Both happen in the same way and for the same reasons, so there is no real reason to differentiate them. When biologists do use different terms, it is simply for descriptive reasons.

When creationists use the terms, however, it is for ontological reasons — this means that they are trying to describe two fundamentally different processes. The essence of what constitutes microevolution is, for creationists, different from the essence of what constitutes macroevolution. Creationists act as if there is some magic line between microevolution and macroevolution, but no such line exists as far as science is concerned. Macroevolution is merely the result of a lot of microevolution over a long period of time.

In other words, creationists are appropriating scientific terminology which has specific and limited meaning, but they are using it in a broader and incorrect manner. This is a serious but unsurprising error — creationists misuse scientific terminology on a regular basis.

A second problem with the creationist use of the terms microevolution and macroevolution is the fact that the definition of what constitutes a species is not consistently defined. This can complicate the boundaries which creationists claim exist between microevolution and macroevolution. After all, if one is going to claim that microevolution can never become macroevolution, it would be necessary to specify where the boundary is which supposedly cannot be crossed.

Conclusion:

Simply put, evolution is the result of changes in genetic code. The genes encode the basic characteristics a life form will have, and there is no known mechanism that would prevent small changes (microevolution) from ultimately resulting in macroevolution. While genes can vary significantly between different life forms, the basic mechanisms of operation and change in all genes are the same. If you find a creationist arguing that microevolution can occur but macroevolution cannot, simply ask them what biological or logical barriers prevent the former from becoming the latter — and listen to the silence.

 

this diagram shows the differences between mirco evolution and macro evolution 

 

 

Here is a video clip comparing Microevolution vs. Macroevolution

 

 

 

This is a good representation of how microevolution occurs, and how it works.