With regard to heterosis, would the following statements be consistent with the dominance hypothesis, the overdominance hypothesis, or both?
A. Strains that have been highly inbred have become monomorphic for one or more recessive alleles that are somewhat detrimental to the organism.
B. Hybrid vigor occurs because highly inbred strains are monomorphic for many genes, whereas hybrids are more likely to be heterozygous for those same genes.
C. If a gene exists in two alleles, hybrids are more vigorous because heterozygosity for the gene is more beneficial than homozygosity of either allele.

When artificial selection is practiced over many generations, it is common for the trait to reach a plateau in which further selection has little effect on the outcome of the trait. This phenomenon is illustrated. Explain why.

In a fairly large population of people living in a commune in the southern United States, everyone cares about good nutrition. All of the members of this population eat very nutritious foods, and their diets are very similar to each other. How do you think the height of individuals in this commune population would compare with that of the general population in the following categories?
A. Mean height
B. Heritability for height
C. Genetic variation for alleles that affect height

The heritability for egg weight in a group of chickens on a farm in Maine is $0.95$. Are the following statements regarding heritability true or false? If a statement is false, explain why.
A. The environment in Maine has very little effect on the outcome of this trait.
B. Nearly all of the phenotypic variation for this trait in this group of chickens is due to genetic variation.
C. The trait is polygenic and likely to involve a large number of genes.
D. Based on the observation of the heritability in the Maine chickens, it is reasonable to conclude that the heritability for egg weight in a group of chickens on a farm in Montana is also very high.

What is the difference between broad-sense heritability and narrow-sense heritability? Why is narrow-sense heritability such a useful concept in the field of agricultural genetics?

From a biological viewpoint, speculate as to why many traits seem to fit a normal distribution. Students with a strong background in math and statistics may want to explain how a normal distribution is generated, and what it means. Can you think of biological examples that do not fit a normal distribution?

The abdomen length (in millimeters) was measured in 15 male Drosophila, and the following data were obtained: $1.9,2.4,2.1,2.0$, $2.2$, 2.4, 1.7, 1.8, 2.0, 2.0, 2.3, 2.1, 1.6, 2.3, and 2.2. Calculate the mean, standard deviation, and variance for this population of male fruit flies.

After 1964, quarters were manufactured so that their weights have a mean of 5.67 g and a standard deviation of 0.06 g. Some vending machines are designed so that you can adjust the weights of quarters that are accepted. If many counterfeit coins are found, you can narrow the range of acceptable weights with the effect that most counterfeit coins are rejected along with some legitimate quarters. If you adjust your vending machines to accept weights between 5.60 g and 5.74 g, what percentage of legal quarters are rejected? Is that percentage too high?

At the molecular level, explain why quantitative traits often exhibit a continuum of phenotypes within a population. How does the environment help produce this continuum?

Li sted below are heights (in.) of mothers and their first daughters. The data are from a journal kept by Francis Galton. Use a 0.05 significance level to test the claim that there is no difference in heights between mothers and their first daughters.

$$\begin{matrix} \text{Height of Mother} & \text{68.0} & \text{60.0} & \text{61.0} & \text{63.5} & \text{69.0} & \text{64.0} & \text{69.0} & \text{64.0} & \text{63.5} & \text{66.0}\\ \text{Height of Daughter} & \text{68.5} & \text{60.0} & \text{63.5} & \text{67.5} & \text{68.0} & \text{65.5} & \text{69.0} & \text{68.0} & \text{64.5} & \text{63.0}\\ \end{matrix}$$

The trait of blood pressure in humans has a frequency distribution that is similar to a normal distribution. The following graph (see next page) shows the ranges of blood pressures for a selected population of people. The red line depicts the frequency distribution of the systolic pressures for the entire population. Several individuals with high blood pressure were identified, and the blood pressures of their relatives were determined. This frequency distribution is depicted with a blue line. (Note: The blue line does not include the people who were identified with high blood pressure; it includes only their relatives.)
What do these data suggest with regard to a genetic basis for high blood pressure? What statistical approach could you use to determine the heritability for this trait?

In your own words, explain the meaning of the term heritability. Why is a heritability value valid only for a particular population of individuals raised in a particular environment?

If you were designing a computer program to recognize important sequences in DNA, what types of sequences would you include? What would you learn from finding these sequences in the DNA? Be as specific as you can.

An animal breeder had a herd of sheep with a mean weight of $254 \mathrm{lb}$ at 3 years of age. He chose animals with mean weights of $281 \mathrm{lb}$ as parents for the next generation. When these offspring reached 3 years of age, their mean weights were $269 \mathrm{lb}$.
A. Calculate the narrow-sense heritability for weight in this herd.
B. Using the heritability value that you calculated in part A, what weight of animals would you have to choose to get offspring that weigh $275 \mathrm{lb}$ (at 3 years of age)?