Terms to know: polygenic trait, quantitative trait, heritability, Fisher's Fundamental Theorem of Natural Selection, directional selection, stabilizing selection, disruptive selection

Questions:

1. For each of the following situations, answer the following two questions:
1.  How much heritability would you expect each of the following traits to have (explain why).
2.  Explain how to test for heritability.  Assume that none of the animals described can be raised in captivity, but that it is possible to capture families (fathers, mothers, and offspring) at appropriate ages to describe their characteristics.  For each situation, draw a graph representing the predicted results (if you are correct about the expected level of heritability) of your test of heritability. Be sure to label the axes.
1.   Number of toes in a species of opossum that is always born with five toes (per foot) but in which toes may be lost to freezing during cold winters.
2. Tongue length in a population of butterflies that use their tongues to get nectar from flowers.  The ability of a butterfly to get nectar depends on the length of its tongue and the length of the flower.  This butterfly has been feeding from flowers of the same length for several hundred generations.
3. Tongue length in a population of butterflies such as the one described in part b, except this time the butterfly feeds from two kinds of flower, one longer, one shorter.  In hot years the short flowers are common; in cold years the long flowers are common.
4. Tail length of a species gecko (lizard) in which tails drop off when the geckoes are grabbed by the tail by predators; tails gradually grow back again after being lost.
5. Tail length in a species of bird in which birds with longer tails find mates earlier but do not survive as well as birds with shorter tails.
2. In a study of a population of dock plants, you find that leaf size is a quantitative trait.  You can hand pollinate dock flowers so you can know the parents of seeds; you can also collect and grow these seeds of known parentage.  How could you determine the heritability of leaf size in a population of dock plants?  (Hint: you should use the mid-parent - offspring regression method AND consider how you could control for any possible environmental effects).
3. In a population of giraffes, you observe that there is phenotypic variation in the color of their brown spots.  You note that all giraffes are born with dark brown spots, and see that those that occur in shady habitats where the spots have less exposure to the sun have darker brown spots as adults than those in sunny habitats with high exposure to the sun.  Based on these observations, do you think the heritability of spot color in giraffes is high or low?  Clearly explain why.  Then explain how you would test your prediction about heritability using a mid-parent offspring regression; clearly explain how you would obtain data to conduct the regression and what you would plot with these data to test your prediction.  Draw the graph that would support your hypothesis. Be sure to label the axes.
4. In a population of turtles, you observe that there is phenotypic variation in the size of the scales on their heads; variation ranges continuously from very small scales through medium sized scales through large scales.  Explain how you would test the heritability of scale size using a mid-parent offspring regression; be sure to clearly explain how you would obtain data to conduct the regression.  Describe what a graph of this regression would look like if heritability is high and what one would look like if heritability is low.  Finally, state which situation (high or low heritability) indicates more genetic variation in scale size present in the turtle population.
5. How have studies of Darwin's Finches have provided information about the maintenance of genetic variation in quantitative traits?
6. You observe that in a population of wild geraniums, plants with many short branches tend to survive and reproduce better than do plants with fewer longer branches.  Over many generations, however, no change occurs in the "branchiness" of geraniums.  Give a possible explanation for this based on heritability, and explain how you could test this hypothesis.
7. Estimating heritability is important because it indicates the possible response of a trait to natural selection.  Why does it indicate this?  Explain how heritability was estimated and how response to selection were studied in each of the following experiments described in your Freeman and Herron (2001):
1.  The Grant's experiments on Darwin's Finches (Chapter 3)
2.  Galen's experiments on alpine skypilots (Chapter 7)
8. Explain why this Fisher's Fundamental Theorem of Natural Selection is expected to be true in most cases, then give as many situations as you can in which Fisher's Fundamental Theorem of Natural Selection is NOT likely to be true.
9. Describe the expected results of directional selection, stabilizing selection, and disruptive selection: how do they affect mean (average) trait value and how to they affect the heritability of the traits subject to selection?
10. Why is it theoretically possible for mutation to be a mechanism for maintaining genetic variation in quantitative traits given that we know that for single locus traits mutation rates are much to slow to be important in maintenance of genetic variation?
11. Stabilizing selection and heterosis are similar in that in both cases, an intermediate phenotype is favored.  Why is it that heterosis maintains genetic variation but stabilizing selection does not?