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Your textbook is HRW's Biology: Principles and Explorations. Find support at http://go.hrw.com/hrw.nd/gohrw_rls1/pKeywordResults?keyword=HX0%20HOME
Find the link to Massachusetts Biology Frameworks at the Department of Education http://www.doe.mass.edu/frameworks/scitech/2001/standards/ls9_101.html
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This lab showed that natural selection made the proportion of light and dark rabbits change. It was fun.
Pulling pairs of beans from a bag, we saw the number of light beans go down so much they disappeared. The graph has the dark line that goes up and the light line goes down. We learned a lot from this lab about traits, adaptation, natural selection, survive & reproduce, dominant, recessive. We didn’t make mistakes because our hypothesis was right. Next, we want to know what would happen if we brought real hawks into the classroom.
How does the hunting style of the Red-tailed Hawk cause the proportions of light and dark rabbits to change?
Red-tailed hawks hunt by sight from above, so darker rabbits are more camouflaged by the shadows of the shrubs in a summer-time meadow … this is a good adaptation and it is the dominant trait. In this lab (a model, not data from a real natural experiment), we imagined that the hawks ate all of the light furred rabbits (gg) in the population, and 25% of the dark furred rabbits (GG or Gg). Our graph shows that this natural selection made the proportion of light rabbits go down about 10% generation after generation, and the dark rabbits go up by the same amount. Our book defines Natural selection as the “process by which populations change in response to their environment.” (p279) The hawks didn’t know if they were eating a GG or Gg dark rabbit. The dark rabbits that survived reproduced in the next generation so the recessive (g) allele stayed in the gene pool of the population. One error we made every generation was having to round off from decimals, so we never knew if we were supposed to take the lower or higher number. Also, this was a model, so we know that there are other predators besides hawks, and that rabbits don’t just die from being eaten. Next, we would want to know what would happen in the winter, or if this was a desert or grassland that had no shrubs.
The hunting style of the red-tailed hawks made the light rabbits go down and the dark rabbits go up. Beans were rabbits, and there were more dominant alleles (dark) rabbits than recessive alleles (light) because you can get a dark rabbit from Gg and GG, and only gg is a light rabbit, so dark rabbits dominate. We picked two beans at a time until we had picked out all of the rabbits, then got rid of all of the light rabbits and ¼ of the dark ones that were their. We counted the ones that were left and graphed the data. The hawks style made them choose the light rabbits more than the dark rabbits, making them survive and reproduce. The dark rabbits had camouflage so that trait went up. The dark gene is dominant, so all of the dark rabbits could have been from both dominant beans or from one dominant and one recessive bean. Our graph showed the light rabbits going down and the light rabbits went up. In the first generation, the light line went down alot, then went up, then went down again. We probably dropped beans on the floor, so the numbers on our graph are not perfect. Natural selection is the gradual, non-random process by which biological traits become either more or less common in a population as a function of differential reproduction of their bearers. (Wikipedia)
In order to receive this credit, you are to complete the following on a clean sheet of paper, stapled to the front of the original…
Unit I.The Practice of Science
- Definition and construction of a hypothesis
- Theory as explanation
- Design of a controlled experiment
- Distinguish dependent from independent variable in a controlled experiment
- Qualities of reliable data
- The perspective/gestalt of science research
- The vital role of objective observation in collecting reliable data
- Graphing: Independent and dependent variables on correct axes, labels & units, setting appropriate axis-scales
- The utility of well-designed models
- The 4 qualities of reliable research: replicable, falsifiable, precise, straightforward
- Distinction between precision and accuracy
- The most reliable theories are solidly supported by experimental results from 3+ branches of a science
- Reliable science uses logic to analyze results and meticulously links cause and effect to describe relationships
- Occam’s razor: All else being held equal, the simplest explanation is usually correct
- Bias: the natural human tendency to wish for desired outcomes, overcome by conducting experiments rigorously and analyzing results honestly