Taxonomy, Evolution and DNA Review
DNA
1. What are the building blocks of DNA?
2. How is DNA similar and different from RNA?
3. What is a “nucleotide”?
4. How do nucleic acid base pairs match up?
5. Which nucleic acid base is not found in DNA?
6. What is the sequence of converting information from DNA to a protein?
The code of a strand of DNA can be “transcribed” and “translated”
7. What does transcribe mean?
8. How do you translate the DNA code?
9. What is a “triplet”?
10. What is a complementary strand?
11. Can you translate a strand of mRNA given a table that includes mRNA triplets? (See worksheet)
Evolution
1. What is the distinction between direct and indirect proof?
2. How is convergent and divergent evolution linked to types of proof of evolution?
3. How can fossils be linked both to gradual and punctuated rates of changes of evolution?
4. What is a trait from Darwin or Lamarcks point of view?
5. How are traits linked to populations and gene frequency?
6. What is speciation and how is it linked to isolation mechanisms?
7. What is the significance of gentic drift, gene flow, and non random mating linked to evolution ( Clue please look at chapter on DNA and Evolution)
Chapter Three Quiz feedback
1) Darwin verse Lamarack
· Lamarack proposed a law of use and disuse
· Lamarack proposed that a trait produced by use and disuse was an acquired characteristic
· The example of the length of the giraffes neck was used to show that the length got longer to access food.
· The individual organism changes due environmental needs
In comparison
· Darwin proposed that changes in living things was due to a process which he called natural selection
· Like farmers select specific traits in agriculture, Darwin said that “Nature” was selecting the traits in living things in the wild. He referred to the selection by humans as call “Artificial selection” and the selection of traits by nature as “natural selection”.
· Darwin used a two part premise to explain how nature selected a trait
· His first “proof” was to show that there was some mechanism that was keeping populations from over populating. Using economist Malthus’s ideas, he proposed that populations do not over populate due to “a struggle for existence”. Put simply, population size was being affected by something.
· His second “proof” was to state that within any population of species, there is a wide range of traits. He did not know the source of these traits but he did notice a diversity in traits. He noted that organisms with survived and were able to pass these traits on were those organism that had a trait that was able to adapt to what was occurring in the natural environment. This idea of competition and survival of the fittest was similarly proposed by Wallace who spoke about traits allow species to compete and survive and then pass along traits.
· Put simply, Darwin said that species do not over populate because there is something limiting that growth, The factor that seemed to limit growth was a Natural Selection of traits that allowed the species to survive and pass those traits onto the next generation. The key point is…nature..the environment is doing the selection.
Using the Galpagos Islands and Finches
So here is how the story should go…
A population of original finches arrives at a new location. In this case an island.
The island is able to support the population both with food, water, and habitat. So the population is able to survive, reproduce and grow. In addition, there are no predators to limit the growth of the population. So the population grows but does not over populate. So there must be a reason why.
Within this population is a diversity in shapes of beaks. Those birds with beaks that are able to eat the food on that island are more likely to survive. Nature is selecting a specific trait. Those who do not have that trait migrated. This introduces the idea of “gene flow” (yes..this is on the test!!!)..something Darwin did not know about.
Those birds who did not have the right beak shape for a specific island could fly to another island. Again..migration and gene flow. On the new island was a different habitat. The species which had a trait that allowed the species to survive and populate on the new island was now being selected by a natural source. Aha..natural selection!
What are the implications of this statement?
The reason why things change with time is governed by a mechanism in which nature is doing the selection. The organism that has the trait that allows it to adapt to a small change in the environment will pass that trait to the next generation. Notice that two key words are being used: survive and adapt.
DNA and Darwin and Lamarck
The theory of Natural Selection was able to propose a feasible explanation as to how and why species change with time. It proposed that “nature” was selecting traits that improved the chance for survival and therefore reproduction.
The idea of a characteristic or a trait was a means to show an adaptation had occurred. The actual source of that adaptation was hidden until the mechanisms of how DNA was discovered.
Mutations are a change in the sequence of nucleic bases within DNA. Mutations can also occur due to missing or extra chromosomes or sequences of DNA changing. Put simply..the source of variation is within the code of DNA.
An example of a favoured mutation is the change in colour of English peppered Moths. When the DNA, which mutated created a black pigmented Moth, the population of black moths increased when predators could not find the moth on dark, charcoal coated trees. When the soot in the air decreased due to cleaner burning of coal, the trees now could show their natural white colour. Those moths that had not adopted the changed DNA were able to now increase their population.
This change in expression of traits lead to a more definitive definition of evolution within biology in respect to a change in allele frequency within a population.
Evidence, mechanisms, rates of change and forming new species.
1. If a population is isolated due to morphology, geography, behavior or ecology it is forming a new species due to an isolation mechanism. Notice that there is now a ..that in singular ..species being formed. So we notice that isolation mechanism is linked to the term speciation.
2. If one species crosses the isolation mechansim, then a new species can be formed. If that product of reproduction is not able to reproduce, it is some times called a hybrid. A hybrid is something new due to mixing two species.
3. Darwin proposed that Nature is selecting traits and this is what is going on to create new species. He did not come up with the term “adaptive radiation”.
4. After the mechanism of how DNA works was discovered and explored, there was now a valid source to explain things like mutations and traits. It has been proposed that a specific segment of DNA is responsible for making a specific protein. This segment has been called “a gene” and the theory is that for one gene there is a specific protein. Introducing this idea into evolution, now we can talk about Gene Flow, Gene Pool, Genetic Drift all linking to a change in populations due to the presence or lack of genetic material.
5. The idea of a gene is now being challenged because it has been discovered that several pieces of DNA code may be involved in making a protein. It is also being proposed that expression of sequences of DNA can also be regulated. So..once again..the reason why things change with time is a theory and subject to scientific inquiry.
Rates of change
There are several examples where Darwin’s mechanism also showed a gradual change in time. This created a group of folks who proposed that things change gradually and the theory put forth was called Gradualism.
In 1972, a new theory was proposed to explain gaps in fossil records and quick changes in evolution. The idea was that a population quickly adapts to adapt and then reaches equilibrium. Think about cell phones and you get the idea real fast. One product sets the pace and others hurry to catch up. If you graph this rapid change you have a line with a large slope followed by a flat horizontal line where there is equilibrium.
Mention equilibrium and the physicist and chemist get all excited. Some physics folks suggested that energy within the system was being used up to a point where there was none left for those who could adapt. Chemist jumped for joy and started getting involved with metabolic rates, equilibrium constants and meanwhile, the biologist knew that all things are connected. Lets think of this as the Three Bear Theorem. Too hot, too cold and then..just right.
Now the question is…is anyone reading these notes. It is a dark and stormy afternoon in Vancouver. The heat has been turned off in my room. I am wearing a sweatshirt and hidden underneath it is a snoopy t shirt that says “dazed and confused”. I am exhausted, cold and my head is full of phlegm. It is Friday and the class before me is taking a physics pre test. A population of fruit flies is now invading my room and some inspired student decided to submerge an electric heating element in one of my fish tanks. Five fish gave their lives two days after remembrance day. Poppies do not grow in aquariums. As predicted, several students did not read my notes and so their quiz marks are less than stellar. If any one can remember what the t shirt I am wearing says, then I will give bonus marks on the next evaluation.
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