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Evolution and Selection 1
Why?
Evolution and Selection What mechanisms lead to changes in the diversity of species on Earth?
People make choices by selecting options they like best. The natural world also “selects” (although not as a conscious decision) when environmental conditions allow organisms with a particular genetic trait to live healthier lives than other organisms. In this activity, we will explore how selection affects populations over time.
Model 1 – Desktop Swab Results
E. coli bacterial variants from culture Variant P
Variant Q Variant R Variant S
E. coli colonies on growth medium without triclosan
E. coli colonies on growth medium with triclosan
- What is the source of the bacteria in the culture tube in Model 1? The bacteria in model 1 comes from the top of a desktop so it most likely came from human sources that have contact with the desk top.
- How many genetic variants of E.coli were present in the culture from the initial swab? There were four genetic variants ofE. coli present in the initial swab.
- What variants of E.coli are found on the dish grown without triclosan? All four variants ofE. coli are found on the dish grown without the triclosan.
- Refer to the dish in Model 1 with the medium that included triclosan.
a. What variants of E.coli are found on the dish grown with triclosan? The only variant ofE. coli found on the dish grown with triclosan is Variant S.
b. What likely happened to the other variants of E.coli on the dish with the medium containing triclosan? The other bacteria was likely killed by the triclosan.
E. coli culture
of desktop
2 POGIL™^ Activities for High School Biology
- Based on its effect on E.coli, why is triclosan used as a cleaning agent? Triclosan is used as a cleaning agent because it kills most variants of bacteria.
- Suppose the desktop swabbed earlier was cleaned with a solution containing triclosan. Would living E.coli remain? Support your answer. If the desktop was cleaned with a solution containing triclosan, some living E. coli would remain because Triclosan does not kill all variants of E. coli. The diagram above shows that 1 variant will survive.
- Suppose the desktop was swabbed again after cleaning it with triclosan over a 9-month school year. When the sample was cultured only variant S was seen.
a. What characteristic does the variant S bacteria have that allows it to remain on the desktop even after several months of treatment with triclosan? The variant S bacteria is resistant to triclosan so it will continue to survive and reproduce, even though you clean it regularly.
b. Is it likely that the bacteria in the new swab were on the desk 9-months ago, or are they off- spring of the original bacteria? The bacteria on the new swab are likely offspring of the original bacteria. c. Propose an explanation for the presence of only variant S on the desktop after so much time. The variant S bacteria is resistant to the triclosan and can therefore continue to live and reproduce over long periods of time.
Read This!
Populations of most living organisms exhibit genetic diversity among individuals. Certain traits in a population give some organisms a greater chance of survival than individuals that lack these traits. Because these traits tend to increase the chance of survival, these individuals may produce more offspring that will also have the trait that favors survival. Over time, the number of individuals within the population pos- sessing the favorable trait increases while the number of offspring with the unfavorable trait decreases.
4 POGIL™^ Activities for High School Biology
- Clean Air Acts were passed by governments of industrialized nations beginning in the mid- 1950s. Use this information to explain why the color of the moth population shifted again. During the 1950’s, the clean air act forced factories, etc. to reduce the amount of soot and other pollutants they were spewing into the atmosphere. Since the amount of soot and smog decreased, the habitat for the moths went back to its original coloring, allowing the light colored moths to blend in and survive predation. This in turn made the dark colored moths easily seen, and therefore easier to eat. Since they were no longer living long enough to pass along the trait, their numbers decreased significantly.
Model 3 – Natural vs. Artificial Selection
- Model 3 traces the lineage of what organisms? Model 3 traces the lineage of dogs, wolves, and coyotes.
- How does Model 3 indicate that all three types of organisms came from a common ancestor? In Model 3, each organism branches off of a single line, indicating that they all came from a common ancestor.
- According to Model 3, wolves (gray and red) are more closely related to what other group—dogs or coyotes? Explain your answer. According to Model 3, wolves are more closely related to dogs than coyotes. This is because both dogs and wolves branch from the same line, whereas the coyotes branch from a previous line. Therefore, dogs and wolves are more closely related and coyotes and wolves are.
- Think about the characteristics of the organisms above.
a. What are some differences that you note between wolves and dogs?
b. What similarities can you identify?
§ – Artificial selection
Evolution and Selection 5
- Modern domesticated dogs arose from wolves through selective breeding by humans.
a. What traits might humans have selected in the common ancestor of dogs and wolves that would account for the differences between dogs and wolves? Human would have selected the traits that were most beneficial to us as humans. For example, less aggressive wolves would be favored over more aggressive wolves because the less aggressive wolves would be less likely to harm humans. b. According to Model 3, what is the name of this type of selection? This type of selection is called artificial selection.
Read This!
The events that lead to changes in groups of organisms are called selection by evolutionary biologists. Charles Darwin (1809–1882) is the person credited with carefully outlining how various changes in populations of organisms might occur through time. He called this process natural selection. Humans participate in selection through selective breeding of plants and animals. This is referred to as artificial selection.
- Is the selection that led to the development of wolves and coyotes an example of natural selection or artificial selection? Explain your choice. The selection that led to the development of wolves and coyotes was most likely natural selection because humans did not chose the traits that led to the speciation of coyotes from the common ancestor.
- Refer to Model 1. Is the selection leading to changes in the E. coli variants natural or artificial selection? Explain your choice. The selection leading to changes inE. coli variants is natural selection because we are not choosing to kill some variants while selection for other variants. TheE. coli is simply responding and adapting to the environment.
- Two differences between red and gray wolves is their color and size. What environmental condi- tions might have resulted in selection for red wolves and gray wolves? Habitat is a huge environmental condition in the selection of the traits and size. The traits were best suited to the individual environments allowing those individuals the ability to survive, reproduce, and pass along their traits.
- Refer to Model 2. Is the selection of moths that blend in to their environment an example of natural or artificial selection? Explain your choice. The selection that led to the moths blending into their environment was natural selection because humans did not breed the moths for that particular trait. The moths with the dark coloring were better suited to their environment so their population increased.
