Inquiry in Action: Interpreting Scientific Papers, Key to Questions
Inquiry in Action: Interpreting Scientific Papers
by Ruth Buskirk and Christopher M. Gillen
Key to Questions
Article 1
Inquiry Figure 16.11: Does DNA Replication Follow the Conservative, Semiconservative, or Dispersive Model?
Key to Questions
1. Meselson and Stahl, California Institute of Technology
2. Proceedings of the National Academy of Science, 1958
3. National Foundation for Infantile Paralysis and the National Institutes of Health
4.
density-gradient centrifugation: separation of a mixture of macromolecules, placed in a concentrated solution of cesium chloride, according to their density in a centrifuge
generation time: the time between the birth of one organism (here, a bacterium) and the birth of its offspring
isotope: one of several atomic forms of an element, each containing a different number of neutrons and thus having a different mass
5. Heavy nitrogen isotopes, N15
6. DNA composed of N15 has greater density. Higher-density material is to the right in the photograph.
7. (a) About one-half; (b) by 4.3 hours, the band of DNA begins to narrow; and by 19.2 hours, the band was fairly narrow; (c) middle.
8. The line with two peaks is a graph of the darkness of the band images in Figure 2a, showing the position of the same two bands along the same horizontal scale of density.
9. They added the growing bacteria culture to a growth medium containing a tenfold excess of N14H4Cl.
10. The density of DNA varies directly with the fraction consisting of N15. Therefore, the relative position of the band between the band of fully labeled DNA and the band of fully unlabeled DNA indicates how much of the DNA was labeled with N15.
11. (a) 0.81 hours for experiment 1 and 0.85 hours for experiment 2; (b) about 3.5 hours for 4 generations; (c) switch bacteria from growth media containing only N15 molecules to growth media containing only N14 molecules.
12. (a) After 1.0 generation, the peak DNA density was lower than the density of initial DNA. (b) After two generations, there were two peaks, and one of those was at the same density as the peak after one generation. (c) None
13. One generation time after the addition of N14, these half-labeled or “hybrid” molecules alone are observed. Thus, all daughter molecules are half-labeled.
14.
(a) /(b) /
(c) /
15. If the two images in each pair were different, there would be two peaks in sketch a.
16. The two chains separate, then each chain serves as the template for the synthesis of its complement.
17. (a) Bases (purines and pyrimidines); (b) You could label the phosphate with a radioisotope of phosphorus, P32, or label the deoxyribose sugar with a radioisotope of carbon, C14.
18. In “conservative” replication, all the atoms of the original DNA molecule would be together in one of the daughter molecules and the other daughter molecule would be made from all new (nonlabeled) atoms.
19. As long as the pairs of nitrogen bases are present in the DNA fragments, we can still see the proportions of heavy and light nitrogen that support the Watson-Crick model of replication.
20. You could label a different part of the DNA molecule, as suggested in question 16, and see if the density results are the same. You could repeat these tests with another species of bacteria or with cells from a eukaryotic organism to see if the results can be generalized to all cells.
Article 2
Inquiry Figure 23.16: Do Females Select Mates Based on Traits Indicative of “Good Genes”?
Key to Questions
1. Welch; University of Missouri; NSF, NIMH, and Sigma Xi
2. Science, 1998
3.
fitness (evolutionary): the relative contribution of an individual to the gene pool of the next generation
gravid: carrying eggs or developing young
half-sibship: a group of individuals that have one parent, but not both, in common
heritable: capable of being passed from parent to offspring; thus, having a genetic basis
multivariate analysis: statistical analysis considering the effects of more than one variable at a time
phenotype: the physical and physiological traits that appear in an organism
sexual selection: natural selection for mating success
4. Gray tree frog, Hyla versicolor; abbreviated as H. versicolor (with just the initial of the genus)
5. The “good genes” model predicts that females can use male courtship displays to select mates with high-quality traits, increasing the likelihood that the females will have high-quality offspring.
6. This separates the effect of direct benefit to the female from the indirect (genetic) benefit of good mate choice.
7. In the field, females freely initiate matings with calling males and do not always choose the first male encountered. Males do not provide direct benefits to the females such as defending oviposition sites, offering nuptial gifts, or contributing parental care.
8. Males that produce long calls spend less time calling per night and attend fewer choruses per season.
9. Long calls appeared to be more costly to the males than short calls, because long-calling males spend less time calling per night and attend fewer choruses per season. Because of the potential costs, investigators thought that males with longer call duration might have higher genetic quality.
10. With maternal half-sibships, maternal effects would be controlled. The offspring would share the same maternal genes, and the only genetic difference would be due to the male.
11. In 1995, nine sets of two males and nine gravid females were used. In 1996, six sets of two males and eleven gravid females were used.
12. Long-callers had 10.1 more pulses per call and called 0.69 seconds longer than short-callers.
The difference in pulses per call was statistically significant at the level of p < 0.001. According to previous work referenced in note 15, female H. versicolor routinely base preferences on differences of as few as two pulses per call, so the measured difference of ten pulses per call is meaningful.
13. Calling effort is the proportion of time in the frog chorus that the individual was producing sound. In both test years, long-callers had a greater calling effort than short-callers.
14. Investigators reared 538 tadpoles in 1995 and 384 in 1996, individually in laboratory containers with 1.0 liter of water. They used two food levels because environmental conditions such as food level can affect relative performance of different genotypes. Investigators assigned tadpoles randomly to food levels and test parameters. The study was blind (the investigators gathering results did not know the genetic identity of the tadpoles they were testing).
15. Performance parameters: larval growth, larval period, metamorphic mass (size at the stage of tail metamorphosis), larval survival, postmetamorphic growth. Offspring of long-callers had better performance.
16. Experimental study
17. Lab study
18. Offspring of males with long calls showed better phenotypic performance than offspring of males with short calls.
19. There is genetically based variation in call duration among males. Males with longer calls produce offspring with greater performance phenotypes. Thus, males with longer calls have greater relative fitness and the proportion of longer-calling males increases in the population.
20. There is genetically based variation in call duration among males. Males with longer calls produce offspring with greater performance phenotypes. Because females who choose and mate with long-caller males will have higher-quality offspring and greater fitness, making this choice will be selected for.
21. Many field and lab studies are possible with this research system. For example, you could do more tests on the effects of rearing tadpoles at different resource levels. You could test whether the rearing conditions of a male (food levels, crowding, etc.) affected his calling duration. You could do a selection experiment and see if over time you could develop two different genetic strains, long-callers and short-callers, with other differences in behavioral traits as well.
Article 3
Inquiry Figure 41.4: Can Diet Influence the Frequency of Birth Defects?
Key to Questions
1. The Lancet, 1980
2. Smithells, Department of Pediatrics and Child Health, University of Leeds
3.
amniocentesis: a prenatal diagnosis technique in which amniotic fluid is extracted from the uterus and tested for certain genetic and congenital conditions in the fetus
neural tube defects (NTDs): conditions such as spina bifida and anencephaly resulting from abnormal development of the neural tube early in fetal development
periconceptional: the period from about one month before to one month after the time of conception
placebo: an inactive substance that resembles the treatment (so experimental subjects do not know whether they are receiving the treatment or the placebo)
vitamin: an organic molecule required in the diet in very small amounts
4. Nutritional factors
5. Women who previously had one or more NTD infants and were planning another pregnancy but were not yet pregnant
6. Women who previously had one or more NTD infants but were either pregnant when referred for the study or declined to take part in the study
7. One hundred eighty-five mothers were in the fully supplemented group. They received a multivitamin and iron preparation three times a day for about a month before conception and into the second month of pregnancy.
8. The investigators did not include data on those women in this study. (They kept the information and included it in their larger analysis.)
9. (a) Pairs were matched by number of previous NTD infants, estimated date of conception, and age. (b) In addition to the variables listed in (a), mothers might have varied by such factors as their baseline nutritional needs, their normal diet, their health, their geographic location, their willingness to follow experimental protocol, how often they saw a physician, and genetic factors.
10. In the supplemented group, there were 140 infants without NTD and 1 with NTD. In the control group, there were 192 infants without NTD and 12 with NTD. The recurrence rate was 11.5% in the group without vitamin supplementation and was 0.6% in the mothers with supplementation.
11. (1) The mothers who volunteered and participated in the supplement study might unknowingly have had a lower risk of NTDs. (2) Mothers receiving vitamin supplementation might have lost more NTD fetuses in miscarriages (spontaneous abortion). (3) Some unknown factor might be at work (such as the previous use of oral contraceptives mentioned in the discussion).
12. Despite the alternative explanations mentioned, the observed difference is sufficient to conclude that vitamin supplementation can prevent NTDs in this group of women. Results can not necessarily be generalized to all women until genetic and environmental factors are understood. A similar study of the effect of vitamins should be done in the general population, not just those who have previously had NTD infants.
13. (a) In randomized trials, the decision of which women to place in the control group and which to place in the treatment group would be based on a random draw rather than on any defined characteristics. (b) A placebo is an inert substance that is not physiologically active but resembles the treatment medication. With use of placebos, a group of women would follow the same treatment schedule as the women receiving vitamins but would unknowingly be taking inactive substances. (c) Individual answers may vary. Lipsett and Fletcher (1983) pointed out that even before 1976 there was information suggesting that vitamin treatments prevented NTDs. If there is good evidence that a proposed treatment is beneficial, it is unethical to withhold it from subjects. Student responses might point out that the correct procedure for a scientific test on humans would be difficult to administer.
14. Many responses are possible here; for instance, one could repeat the analysis with pairs of control and supplemented mothers who are matched for one of the uncontrolled variables mentioned in question 9(b). In addition, one could repeat this study comparing different parts of the world, perhaps including a region where NTDs are more prevalent. Another approach is to test different components of the vitamin supplement separately to see which element is most effective in preventing NTDs.
Article 4
Inquiry Figure 56.14: What Caused the Drastic Decline of the Illinois Greater Prairie Chicken Population?
Key to Questions
1. Science, 1998
2. Illinois Natural History Survey, Illinois Department of Natural Resources, Douglas-Hart Nature Center, University of Illinois
3. Tympanuchus cupido pinnatus, grassland
4.
extinction vortex: a downward population spiral leading to extinction
microsatellite markers: highly variable DNA sequences, not associated with gene loci coding for specific proteins, that are used to estimate genetic diversity
allele: a specific version of a gene
clutch: the set of eggs laid by a female and incubated at one time
extirpation: destruction, elimination
lek: a mating arena where males display and court entering females
radiotelemetry: a method for locating and tracking individual animals wearing devices that emit radio signals
recruitment: addition of individuals to the population through birth and immigration
5. Low genetic variation decreases fitness and also makes a population less able to respond to environmental change. In a small population, chance events could prevent breeding in an entire generation or kill the most productive individuals, thus limiting population growth.
6. Loss of habitat suitable for reproduction
7. The number of males fluctuated between 40 and 84 in the 1960s, increased to a high of 206 males in 1972, and dropped to 5 or 6 in 1994.
8. The y-axis label is “Eggs hatched (%)”; circles. High, 100%; and low, 38%. Vertical bars show one standard error (SE is a statistical measure of the spread of values around the mean value) above and below the mean, and adjacent numbers indicate number of nests.
9. Factors include abandoned nests, researcher disturbance, nest parasitism by ring-necked pheasants, and eggs that were incubated but infertile, among other things.
10. Managers started a translocation program, moving 271 male and female prairie chickens from large populations in Minnesota, Kansas, and Nebraska to Jasper County, Illinois. Poor reproduction and low numbers in the Illinois population led them to do this manipulation. The objective was to increase both the numbers and genetic diversity in the Illinois population.
11. After each year, 25%–67% of the transplanted prairie chickens survived and integrated into the breeding population. After two years, the mixed populations had bred and the spring 1996 count of breeding males had risen to 70.
12. (a) The number of males was between 5 and 20 in 1987–1989 and around 30 in 1995–1997. (b) The percentage of eggs hatched was around 70%–80% in 1987–1989 and around 90%–100% in 1995–1997.
13. Probably (a) number of males is a better indicator of the population size, because it represents an actual sample of the individuals present, and (b) percentage of eggs hatched is a better indicator of genetic diversity, because the nonviable eggs include individuals that are homozygous for harmful recessive alleles as a result of inbreeding.
14. Rainfall that is excessive or too low, flooding
15. Successful clutches from individuals in Illinois × Illinois crosses during the same seasons
16. Field study
17. Observational study. The translocation of individuals could be viewed as a manipulation, but it was not set up as a controlled experiment.
18. They concluded that sufficient genetic diversity was more important, because the percentage of eggs that hatched increased greatly when individuals from other populations were integrated into the breeding population.
19. One possible way is to study for comparison prairie chicken reproduction in Minnesota or Nebraska, where the species is more widespread. You could study populations that vary in number but not diversity levels or populations of similar numbers that vary in genetic diversity.
20. Some examples: You could acquire data on reproduction in prairie chickens in Minnesota or Nebraska, where populations are larger. In the Illinois population, you could follow the history of marked individuals and compare individual birds’ microsatellite diversity measures with their breeding success. You could supplement the food or habitat of a population and measure how that affects breeding success in the population.
Article 5
Inquiry Figure 1.27: Does the Presence of Venomous Coral Snakes Affect Predation Rates on Their Mimics, Kingsnakes?
Key to Questions
1. Nature, 2001
2. Pfennig, Harcombe, Pfennig; University of North Carolina
3.
Batesian mimicry: palatable species that resemble dangerous species are protected from predation
sympatric: in the same geographic location
allopatric: in a different geographic location
4. Snakes: Micrurus fulvius, eastern coral snake; Lampropeltis triangulum, scarlet kingsnake; Micruroides euryxanthus, western coral snake; Lampropeltis pyromelana, sonoran mountain kingsnake
5. Protection should break down in areas where the dangerous model is absent.
6. Pre-colored plasticine threaded onto a wire
7. At each site, investigators placed ten triplets of one ringed, one striped, and one plain brown snake models.
8. North Carolina and South Carolina tests included eight sympatric sites and eight allopatric sites. Arizona tests included 14 sympatric and 10 allopatric sites.
9. Figure 1a: x-axis latitude and y-axis “proportion of total attacks on ringed replicas.” Figure 1b: x-axis elevation and y-axis “proportion of total attacks on ringed replicas.”
10. In North Carolina and South Carolina, coral snakes are present at latitudes south of 35°N and became increasingly rare with increasing latitude. In Arizona, coral snakes are present at elevations below 1,770 feet.
11.
(a) Lower
(b) Lower
12.
(a) No difference
(b) No difference
13. Attack rates on ringed replicas are higher in areas where coral snakes are absent.
14. Yes
15. No
16. (B)
17. Attack rates on ringed replicas are higher in areas where coral snakes are absent.
18. Yes
19. No
20. (B)
21. Experimental study