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1 .Listen to part of a lecture in a biology class.
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2 .Today, I want to discuss the changes that occur when some members of the species move into a new habitat.
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3 .Say, some green snakes move from a grassy area to a dry, rocky one where nothing is green.
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4 .The green coloration that helped the snake avoid predators in the grassy area is no longer effective.
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5 .Instead, snakes with brownish pigmentation are more likely to survive.
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6 .So the snakes in this new habitat will tend to develop a brownish coloration over time.
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7 .It\'s widely accepted among evolutionary biologists that these types of adaptations occur, but we don\'t know much about the specific details of how they unfold.
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8 .For example, how quickly does this type of evolutionary change occur?
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9 .What exactly is occurring at the genetic level?
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10 .Are multiple changes occurring simultaneously?
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11 .And you know, it\'s only due to recent advances in technology, especially in DNA analysis, that we\'re finally able to answer some of these questions.
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12 .This is a relatively new field of study, and researchers are just beginning to get results from experiments focusing on evolutionary processes within genes, giving us a better understanding of the link between genotype and phenotype.
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13 .Genotype refers to the genetic makeup of an individual, whereas phenotype refers to an animal\'s appearance, the visible characteristics that result from an individual\'s genes.
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14 .Until recently, we could only observe evolutionary changes from the outside at the phenotype level.
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15 .But now we can also follow evolutionary changes in the genotype of a population.
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16 .Let\'s look at an experiment that involved a species of deer mouse that lives in the sand hills of Nebraska.
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17 .Now it might seem kind of hard to get excited about deer mice, seeing as they\'re the predominant mammal in North America, but this particular mouse population stands out because unlike its dark haired neighbors, it\'s light colored.
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18 .Most of Nebraska\'s soil is dark and dark haired mice are very common, but this particular area of Sand Hills has a lighter terrain inhabited by light colored mice.
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19 .The experiment tracked pigmentation change to learn more about how organisms adapt to their environment.
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20 .The hypothesis was that the population in the sandy area had evolved from dark fur to light because a lighter coat for greater fitness by camouflaging and protecting the mice from predators like owls.
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21 .The term fitness in an evolutionary context, refers to the ability of individuals to survive and reproduce, and fitness can actually be measured.
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22 .By tracking the spread of light colored fur over time, the researchers were able to quantify the amount of fitness that this trait provided the mice.
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23 .Several identical enclosures were erected for this experiment, but some were set up on light colored sand, while others were placed on dark soil.
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24 .The researchers collected both dark and light colored mice in the wild, weighed and measured them, and collected samples of their DNA.
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25 .Then they placed both types of mice inside these closed areas.
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26 .Each enclosure held 50 dark and 50 light mice.
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27 .The mice were tested every two months to track how the genotype of this mixed population would evolve in each environment and to monitor the rate of change.
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28 .Now you might think we couldn\'t see genetic changes this quickly, but deer mice reproduce rapidly, and two months can produce two new generations.
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29 .Researchers were looking for changes in the frequency of certain genotype.
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30 .That\'s what evolution is all about.
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31 .Remember that green snake I mentioned earlier, and the changes it might go through?
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32 .The researchers hope to track all the genetic changes happening in the deer mouse population over the course of the experiment and record if and how these changes were expressed in the outward appearance of the mice.
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33 .As expected, one change was in the frequency of the genetic variant responsible for coat color.
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34 .In the light environment, the frequency of the gene responsible for the light colored coat gradually increased and spread throughout the population.
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35 .The team could measure the exact speed with which this happened.
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36 .The more surprising result was that many genes not related to pigmentation also changed during the experiment, indicating that other evolutionary changes were occurring as well.
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37 .The problem is that while we know these other genetic variants must be associated with greater fitness, we don\'t really know how.
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38 .Do they make the mice faster, improve their ability to procure food, or is it something else entirely?
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