Research Methods in Biology
Homework 3
Due Tuesday, Sept. 18

You must type this and all other homework assignments. Do not e-mail the assignment to me; turn it in early (at 322 Wolf) for a foreseeable absence, or turn it in late after an unexpected absence from class.

  1. As I was typing this assignment, our cat Gus wanted me to pet him, so he patted me on the arm with his left paw 9 times and his right paw 2 times. Is this significantly different from a 1:1 ratio? Analyze the data using all four of the goodness-of-fit tests we've learned, report the P-values, and write a sentence interpreting the results.
  2. Falk and Ayala (1971) collected data on 1187 individuals, recording whether each one clasped their hands with the right thumb on top (R) or the left thumb on top (L). There were 535 R individuals and 652 L individuals. Is this significantly different from a 1:1 ratio of R and L individuals? Try to analyze the data using all four goodness-of-fit tests, report the P-values, and write a sentence interpreting the results.
  3. Write a sentence or two comparing your results from questions 1 and 2.
  4. When I come home in the evening, Gus the cat is usually sleeping on the couch. Our couch has 4 cushions of equal size. Imagine I record the cushion that Gus is sleeping on for 14 days, and get the following: 7 times on the far left cushion, 3 times on the middle left, 0 times on the middle right, and 4 times on the far right. Is Gus sleeping on the cushions randomly? Analyze the data using all three appropriate tests. For the randomization test, use at least 1000 replicates (and be sure to report how many replicates you used).
  5. The CVJ5 locus has two alleles, L and S, in the oyster Crassostrea virginica. In a sample of 60 oysters from Panacea, Florida, there were 49 L alleles and 71 S alleles; a sample of 60 oysters from Charleston, South Caroline had 43 L alleles and 77 S alleles (McDonald et al. 1996). Analyze these data: give a biological question the data could be used to address, and state your statistical null hypothesis and alternative hypothesis. Analyze the data using the appropriate test, and interpret the results.
  6. Falk and Ayala (1971) recorded the following data on the hand-clasping of parents and offspring: where both parents were R, there were 147 R and 145 L offspring; where both parents were L, there were 118 R and 180 L offspring; where one parent was R and the other was L, there were 270 R and 327 L offspring. Analyze these data: give a biological question the data could be used to address, and state your statistical null hypothesis and alternative hypothesis. Analyze the data and interpret the results.
    Here are three practice questions for the exam. For each experiment, give the appropriate statistical test. If either a chi-square test or a G-test is appropriate, you must pick one or the other. If your answer is a chi-square or G-test, you must say whether it is a goodness-of-fit test or a test of independence.
  7. You genetically engineer mice to knock out a gene you think is involved in cell division. You have 40 mice with the +/- genotype (one chromosome is missing the gene) and 50 mice with the -/- genotype (the gene is missing from both chromosomes). You give all the mice a dose of radiation, then 12 months later you cut the mice open and see how many have cancer. Six of the +/- mice have cancer, while 11 of the -/- mice have cancer.
  8. You want to know whether births are spread evenly throughout the year. You go to the Deer Park on a Friday night and ask everyone what month they were born in. You record data for a total of 98 people.
  9. You are studying the eyeless gene in Drosophila melanogaster. Homozygotes for the mutant allele have smaller eyes than wild-type flies, with the amount of reduction in eye size being variable among flies and even between eyes. You examine 70 mutant homozygotes, and 31 have the right eye smaller than the left, while 39 have the left eye smaller.

References

Falk, C.T., and F.J. Ayala. 1971. Genetic aspects of arm folding and hand-clasping. Japanese journal of human genetics 15: 241-247.

McDonald, J.H., B.C. Verrelli and L.B. Geyer. 1996. Lack of geographic variation in anonymous nuclear polymorphisms in the American oyster, Crassostrea virginica. Molecular Biology and Evolution 13: 1114-1118.

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This page was last revised September 12, 2007. Its URL is http://udel.edu/~mcdonald/stathw3.html