Quantitative and Behavior Genetics

1) Phenotypic variation does not "match-up" exactly with any one type of genetic influence. In other words, we can't simply 'look' at the distribution of phenotypic variation and know whether or how genes might be involved in that expression. For example, provide eaxamples of how a discontinuous trait could be entirely genetic or entirely environmental.

2) One example that I did NOT mnetion in class was a continuous trait influenced by a single gene. Look up "expressivity" again, like with the Drosophila mutation 'bar eye', to see such an example.

3) How might you use a 'common garden' experiment, or any controlled laboratory environment, to assess the heritability of a trait? Make reference to Vp, Vg, and Ve.

4) Why would it be dangerous to generalize from this experiment to another population? Include the concept of a 'genotype x environment' interaction.

5) Suppose you are an cattle rancher, and you want to produce big cattle. You observe that there is some variation in body size in your herd, but you don't know if it is due to genetic variation among the cattle or the environmental varation caused by differences in diet. Before you invest millions on a new breeding program or in more nutritious fodder, you decide to do a little selection experiment to see what the heritability of body size is. Controlling for body size differences in your cows and bulls, the average body size in your herd is 1500 lbs, but you find a few cows and bulls to breed that average 2000 lbs. When mature, their calves weigh 1600 lbs. What is the heritability of body weight in your herd? If you can increase mean body weight by 10% with a more nutritious feed that is only 5% more expensive, should you invest in a breeding program or new fodder?

6) In one type of MZ-DZ comparison, phenotypic variation between MZ twins raised together is assumed to be environmental, and equal to the environmental variation that DZ twins raised together experience. If this is true, how might you calculate the Vg for this trait in the DZ twins? Why might this assumption be false,and what effect would that have on your estimate of genetic contribution to this trait?

7) In 'twins raised apart' studies, what are the methods and assumptions, and how do we ascertain that a trait has a significant genetic contribution?

8) Why should we expect behaviors to be multifactorial (influenced by environment and genetics)?