bio chap 18 Flashcards Preview

Biology 1 > bio chap 18 > Flashcards

Flashcards in bio chap 18 Deck (45):
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).

31

Define the “heritability” of a trait and explain why it depends on the population being studied.

Heritability of a trait is the proportion of the total variation due to genetic differences among individuals. Heritability depends on the population being studied because the influence of the environment and the genotypes of the populations are going to be different for different populations or even the same population at different times. Thus, these factors change the relative heritability of that complex trait.

32

Define “concordance” and explain how twin studies can be used to investigate the importance of genetic and environmental factors in the expression of a trait.

Concordance is defined as 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. Identical twin studies can be used to investigate the importance of environment and genetic factors in the expression of a trait because both twins have the same genotypes. The variable in this situation is the environment; the researcher must be able to tease apart effects of genes and environment on a particular trait.

33

For a typical complex trait, describe the relationship between the number of genes affecting the trait and the magnitude of their effects on the trait.

When few genes contribute to a trait, each one typically has a large effect. Conversely, when many genes contribute to a trait, each one typically has a small effect.

34

Explain what personalized medicine is and how it relates to complex traits such as human diseases.

Personalized medicine is when the patient’s genotype for a particular disease is known and a treatment is matched specifically to the genetic risk factors of that patient.

35

All genotypes are equally susceptible to the effects of a high-fat diet.

false

36

Genetic differences are always more important than environmental differences for determining phenotypic outcomes.

false

37

Which of the following statements is true regarding "heritability"?

**Heritability is the measure of whether a trait can be passed from parents to offspring in a given population.
**A heritability of 100% means that a certain trait―if present in the parental generation―will always be observed in the progeny.
**A heritability of 0% means that any variation observed for a trait in a given population is the result of genetic―not environmental―factors.
**If the heritability of a given trait in a population is 100%, then the heritability of that trait for all populations will be 100% (i.e., heritability is constant across different populations for the same trait).
ALL OF THESE ARE FALSE

38

A concordance of 50% for a trait occurring in identical twins only provides evidence for the role of nature or genes in the development of this trait, and does not yield any information regarding the role of nurture or environment in this trait.

false

39

Genetic and environmental influences do not interact or contribute to the phenotypic outcomes in precise ways.

false

40

If all of the variation in a trait in the population is due to differences in the environment, then the mean phenotype of the offspring would be independent of parental phenotype and would be identical to the mean phenotype of the population.

true

41

If genetically different strains of corn are grown in a greenhouse and subject to identical environmental conditions, then differences in height would be due to genetic differences and:

the heritability measure would be 100%.

42

When studying phenotypic variations due to the environment, it is necessary to compare organisms with identical genotypes. In addition, it is necessary to use identical environments when studying variation in genotypes.

true

43

For which of the following traits would the difference between the concordance rates seen in fraternal and identical twins be the greatest?

autism

44

Twin studies have been used to assess the relative importance of "nature" versus "nurture" in determining variation among individuals for complex traits. Which of the following statements is not correct?

Twin studies show that autism and clinical depression are not significantly influenced by genotype.

45

For which of the following traits do genetic factors not play a major role in the development of the trait?

cancer (at nonspecific sites)