Evolutionary Analysis: Global Edition

Jon C. Herron, Scott Freeman, Jason Hodin

Chapter 9

Evolution at Multiple Loci: Quantitative Genetics - all with Video Answers

Educators

Chapter Questions

Problem 1

Degree of antisocial behavior is a quantitative trait in human males. Avshalon Caspi and colleagues (2002) used data on several hundred men to investigate the relationship between antisocial behavior and two factors. The first factor was genotype at the locus that encodes the enzyme monoamine oxidase $A(M A O A) .$ MAOA acts in the brain, where it breaks down a variety of the neurotransmitters nerve cells use to communicate with each
other. The gene for MAOA is located on the X chromosome. Due to genetic differences in the gene's promoter, some men have low MAOA activity and others have high MAOA activity. The second factor was the experience of maltreatment during childhood. Based on a variety of evidence, the researchers determined whether each man had experienced no maltreatment, probable maltreatment, or severe maltreatment. The data are summarized in Figure 9.34.
a. Is the variation among men in antisocial behavior at least partly due to differences in genotype? Explain.
b. Is the variation among men in antisocial behavior at least partly due to differences in environment? Explain.
c. Do men with different genotypes respond the same way to changes in the environment? Explain.
d. Is antisocial behavior heritable? Explain.
e. Do these data influence your opinion about how men who exhibit antisocial behavior should be treated
and/or punished?

John Barone

John Barone

Numerade Educator

Problem 2

The serotonin transporter is a cell-surface protein that recycles the neurotransmitter serotonin after it has been used to carry a message between nerve cells in the brain. There are two alleles of the serotonin transporter gene: $s$ and $l .$ Klaus-Peter Lesch and colleagues (1996) found that people with genotypes $I s$ and $s s,$ score slightly, but significantly, higher than people with genotype $I l$ on psychological tests of neuroticism (see Figure 9.35 ).
a. Are these data consistent with the hypothesis that the serotonin transporter gene is a QTL that influences neuroticism? Explain.
b. Is the serotonin transporter gene the gene for neuroticism? Explain.
c. Can you think of another plausible explanation, in which the serotonin transporter gene plays no role at all in neuroticism? Explain.

John Barone

Numerade Educator

Problem 3

There are three modes of selection. They operate under different parameters and all of them increase fitness. Which mode of selection maintains genetic variations best and is best suited for evolution?

John Barone

Numerade Educator

Problem 4

Suppose you are telling your roommate that you learned in biology class that within any given human population, height is highly heritable. Your roommate, who is studying nutrition, says, "That doesn't make sense, because just a few centuries ago most people were shorter than they are now, clearly because of diet. If most variation in human height is due to genes, how could diet make such
a big difference?" Your roommate is obviously correct that poor diet can dramatically affect height. How do you explain this apparent paradox to your roommate?

John Barone

Numerade Educator

Problem 5

Now consider heritability in more general terms. Suppose heritability is extremely high for a certain trait in a certain population.
a. First, can the trait be strongly affected by the environment despite the high heritability value? To answer this question, suppose that all the individuals within a certain population have been exposed all their lives to the same level of a critical environmental factor. Will
the heritability value reflect the fact that the environment is very important?
b. Second, can the heritability value change if the environment changes? To answer this question, imagine that the critical environmental factor changes such that different individuals are now exposed to different levels of this environmental factor. What happens to variation in the trait in the whole population? What happens to the heritability value?

John Barone

Numerade Educator

Problem 6

A dog breeder has asked you for advice. The breeder keeps Alaskan huskies, which she races in sledding events. She would like to breed huskies that run faster. The table below gives data on the running speeds $(\mathrm{m} / \mathrm{s})$ of 15 families of dogs in the breeder's kennel.
$$\begin{array}{ccc}
\text { Family } & \text { Midparent } & \text { Midoffspring } \\
1 & 12.7 & 10.8 \\
2 & 7.6 & 8.0 \\
3 & 14.4 & 8.0 \\
4 & 4.3 & 9.7 \\
5 & 11.3 & 6.6 \\
6 & 12.5 & 6.2 \\
7 & 8.9 & 12.5 \\
8 & 8.2 & 7.4 \\
9 & 6.3 & 3.4 \\
10 & 12.7 & 6.7 \\
11 & 13.9 & 7.9 \\
12 & 7.3 & 13.6 \\
13 & 5.9 & 7.4 \\
14 & 12.8 & 12.1 \\
15 & 12.5 & 11.3
\end{array}$$
a. Use a piece of graph paper to prepare a scatterplot of midoffspring values versus midparent values. Approximately what is the heritability of running speed in the breeder's dog population?
b. If the breeder selectively breeds her dogs, will the next generation run substantially faster than the dogs she has now?
c. $W$ hat else would you suggest the breeder should try if she wants to win more races?

John Barone

Numerade Educator

Problem 7

The ability to survive and reproduce is key for a species in order to evolve. The more offspring produced by a species under ideal conditions, the more their chances of survival. Offspring with suitable variations would survive and adapt better to the environment compared to those that do not possess such variations. A greater number of offspring would mean better chances of having ones with favorable variations. Thus, variations in the ability to reproduce and survive would decide how a species would behave in time. Can you discuss how variations in survival and/or reproductive success could be measured?

John Barone

Numerade Educator

Problem 8

In our discussion of Weis and Abrahamson's work on goldenrod galls (data plotted in Figure 9.28 ), we mentioned that the researchers established that there is heri-
table variation among flies in the size of the galls they induce. How do you think Weis and Abrahamson did this? Describe the necessary experiment in as much detail as possible.

John Barone

Numerade Educator

Problem 9

Given the strength of selection that bumblebees exert on alpine skypilots, why haven't flower corollas in the tundra population evolved to be even larger than they are now? Develop at least two hypotheses, and describe how you could you test your ideas.

John Barone

Numerade Educator

Problem 10

Some traits are inherited through generations; some are influenced by the environment over generations; some are expressed in terms of clear expression, whether dominant or recessive; and some are the product of cumulative expressions of many genes. Considering this, how will you distinguish between qualitative and quantitative traits?
evolution?
b. Which of these are more effective for the survival of
a species?

John Barone

Numerade Educator

Problem 11

For an analysis identifying QTLs involved in the local adaptation of pea aphids to different crops, and consideration of the role genetic correlations may play in speciation, see:

DA

Danielle Aguilar

Numerade Educator

Problem 12

For a study in which researchers used quantitative genetics to predict how behavior in a bird might evolve in response to global warming, see:

Caroline Jones

Numerade Educator

Problem 13

How far and how fast can directional selection on a quantitative trait shift the distribution of the trait in a population? For one answer, see:

Jennifer Stoner

Jennifer Stoner

Numerade Educator

Problem 14

As genome-wide mapping techniques become increasingly sophisticated and cost effective, QTLs are rapidly being identified for many human diseases. For some examples, see:

Josee Pacheco

Numerade Educator

Problem 15

For further information on genetic and environmental effects on human intelligence, see:

Alyssa Mae L.

Numerade Educator

Problem 16

For study mapping quantitative trait loci that influence burrowing behavior in a pair of closely related mice, see:

Joanna Quigley

Numerade Educator