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1

On average, what percentage of alleles present in the parents are expected to be shared between identical twins?

100%

2

On average, what percentage of alleles present in the parents are expected to be shared between fraternal twins?

50%

3

In a comparison of ID and FR twins, which is the test group and which is the control group?

ID is the test group, FR is the control group.

4

In a hypothetical study of 50 pairs of FR twins, 30 pairs have only one twin exhibiting some trait and 20 pairs have both twins exhibiting the trait. What is the twin concordance in this case?

40%

5

In a study of macular degeneration (an age-related progressive narrowing of the field of vision), 1000 pairs of ID twins were examined. A total of 14 cases were observed in which at least one of the twins was affected, and in all cases both twins were affected. What is the concordance of this trait for ID twins?

100%

6

In the same study of macular degeneration described in Question 5, 1000 pairs of FR twins were examined. A total of 15 cases were observed in which at least one of the twins was affected, and in six cases both twins were affected. What is the concordance of this trait for FR twins?

40%

7

Suppose the presence or absence of a trait is determined almost exclusively by genetic differences among individuals. What would you expect the concordance of the trait to be for ID and FR twins?

100% for ID twins and less than 100% for FR twins

8

Suppose the presence or absence of a trait is determined almost exclusively by environmental differences among individuals. What would you expect the concordance of the trait to be for ID and FR twins?

Less than 100% for ID twins and the same percentage for FR twins

9

COMPLEX TRAITS ARE THOSE INFLUENCED BOTH BY THE ACTION OF MANY GENES AND BY ENVIRONMENTAL FACTORS.

a

10

Complex traits that are measured on a continuous scale, like human height, are called quantitative traits.

a

11

It is usually difficult to assess the relative roles of genes and the environment (“nature” vs. “nurture”) in the production of a given trait in an individual, but it is reasonable to consider the relative roles of genetic and environmental variation in accounting for differences among individuals for a given trait.

a

12

The relative importance of genes and environment in causing differences in phenotype among individuals differs among traits. For some traits (like height), genetic differences are the more important source of variation, whereas for others (such as cancer), environmental differences can be the more important.

a

13

Genetic and environmental factors can interact in unpredictable ways, resulting in genotype-by-environment interactions.

a

14

GENETIC EFFECTS ON COMPLEX TRAITS ARE REFLECTED IN RESEMBLANCE BETWEEN RELATIVES.

a

15

In an analysis of heights of parents and offspring, Galton observed regression toward the mean, in which the offspring exhibit an average phenotype that is less different from the population mean than that of the parents.

a

16

“Heritability” refers to the proportion of the total variation in a trait that can be attributed to genetic differences among individuals.

a

17

The heritability of the same trait can differ among populations because of differences in genotype or environment.

a

18

TWIN STUDIES HELP SEPARATE THE EFFECTS OF GENOTYPE AND ENVIRONMENT ON VARIATION IN A TRAIT.

a

19

Monozygotic, or identical, twins result from the fertilization of a single egg and are genetically identical.

a

20

Monozygotic, or identical, twins result from the fertilization of a single egg and are genetically identical.

a

21

Concordance is the percentage of cases in which both members of a pair of twins show the trait when it is known that at least one member shows it.

a

22

Comparisons of concordance rates of identical twins and concordance rates of fraternal twins can help to determine to what extent variation in a particular trait has a genetic component.

a

23

MANY COMMON DISEASES AND BIRTH DEFECTS ARE AFFECTED BY MULTIPLE GENETIC AND ENVIRONMENTAL RISK FACTORS.

a

24

Complex traits are often influenced by many genes with multiple, interacting, and unequal effects.

a

25

Give three examples of a complex trait.

Examples of a complex traits are height, weight, hair color, skin color, heart disease, diabetes, cancer, depression, high blood pressure, number of eggs laid by hens, milk production in dairy cows, and yield per acre of grain.

26

Explain why complex traits are often called quantitative traits.

Complex traits are often called quantitative traits because phenotype is measured along a continuum with only small intervals between similar individuals. In many complex traits the phenotype is determined by measurement.

27

Name several factors that influence variation in complex traits.

Several factors that can influence variation in complex traits are environmental factors like sunlight, moisture or nutrition, and genetic factors such as multiple genes affecting a single trait.

28

Explain why it does not make sense to try to separate the effects of genes (“nature”) and the environment (“nurture”) in a single individual.

It does not make sense to try and separate the effects of genes and the environment in a single individual because they are so intimately related that it would be nearly impossible, and mostly meaningless, to split them apart.

29

Explain how you would go about determining the relative importance of genes and the environment for a particular trait.

Let’s say you wanted to test the effects of diet on diabetes development in two sets of mice with different genotypes. Fed a normal diet, the two mice strains have normal levels of blood glucose, but when fed a high-fat and sugar diet, one mouse genotype displays diabetic symptoms while the other does not. This experiment separates the environmental influence of diet on a particular complex trait, diabetes, and shows that both the environment and genotype are important for the development of disease.

30

Define what is meant by “regression toward the mean.”

Regression toward the mean explains that offspring exhibit an average phenotype that is less different from the population mean than that of their parents. Or, in other words, children of short parents tend to be closer to the population mean height (i.e., taller than their parents).