Chapter 17 Launchpad
The concordance rates for four different traits among pairs of MZ and DZ twins were studied, giving the following results. Which answer option explains why concordance rates for some traits may be higher among DZ twins than MZ twins? a. The environment has the same amount of influence on all traits for DZ twins. b. Only environmental influence on the trait can be determined from MZ twin studies. c. DZ twins can only have 50% concordance rates, because they are related by 50%. d. The environment has a large influence on expression of the trait.
d
_____ is defined as the percentage of cases in which both members of a pair of twins show a trait when it is known that at least one member shows it. a. Accordance b. Pleiotropy c. Discordance d. Concordance e. Epistasis
d
Lindsay and Joy are twins that share the same genetic material and appear so similar that their teachers cannot tell them apart. Lindsay and Joy are most likely monozygotic twins. true false
true
For which of these traits do genetic risk factors transmitted from parent to offspring not play a major role in the development of the trait? a. handedness b. epilepsy c. rheumatoid arthritis d. blood pressure e. asthma
a
If the concordance rate for a given trait is 10% for both identical and fraternal twins, this means that: a. genes play a relatively minor role in the development of this trait, whereas environment plays a major role in the appearance of this trait. b. genes play a major role in the development of this trait, and the effect of environment in the appearance of this trait is negligible. c. 10% of twins show the trait. d. based on these data, you can make no statements regarding the role of either genes or environment in the manifestation of this trait. e. genes and environment contribute equally to the development of this trait.
a
Five varieties of hybrid corn are studied for average yield of corn (the phenotype) as a function of annual rainfall (the environment), with the results shown here. a. normalizing transformation. b. genotype-by-environment interaction. c. norm of reaction. d. normal curve. e. normative assessment.
c
In a study of concordance, a sample of identical twins was evaluated for adult-onset diabetes. The following data were collected for this trait: (1) in 36 identical twin pairs, both showed adult-onset diabetes. (2) in 40 identical twin pairs, only one showed adult-onset diabetes. (3) in 336 identical twin pairs, neither showed adult-onset diabetes. These data imply that the environment is an important component of adult-onset diabetes. true false
true
Red coloration in wheat seeds is a complex trait influenced by three unlinked genes, each with two different alleles A and a; B and b; C and c. The Punnett square shown provides the results of a mating between two plants that are both heterozygous at all three loci. Each dominant allele, represented by an uppercase letter, contributes to the red coloration. true false
true
Red coloration in wheat seeds is a complex trait influenced by three unlinked genes, each with two different alleles A and a; B and b; C and c. The Punnett square shown provides the results of a mating between two plants that are both heterozygous at all three loci. The gene products from the dominant genes are additive in their influence on red coloration. true false
true
Red coloration in wheat seeds is a complex trait influenced by three unlinked genes, each with two different alleles A and a; B and b; C and c. The Punnett square shown provides the results of a mating between two plants that are both heterozygous at all three loci. The gene products from the dominant genes are additive in their influence on red coloration. true false
true
When studying phenotypic variation due to the environment, it is useful to compare organisms with identical genotypes. In addition, it is useful to have identical environments when studying variation due to differing genotypes. true false
true
Let us symbolize each member of a MZ twin pair as an "X" if the member shows the trait and as an open square (◻) if the member does not show the trait. Then, in any sample of MZ twins, there are three possibilities, illustrated with data for type 2 diabetes: - X X 20 MZ twin pairs, both members showing the trait - X ◻ 30 MZ twin pairs, only one member showing the trait - ◻ ◻ 500 MZ twin pairs, neither member showing the trait Which twin pairs provide the researchers with no information they can use for a concordance study? a. the 30 twin pairs in which only one twin shows the trait b. the 20 twin pairs in which they both show the trait c. the 500 twin pairs in which neither twin shows the trait d. None of the other answer options is correct.
c
Review Table 17.1 and identify the concordance rates for handedness, measles, and death from acute infection for MZ and DZ twins. Which statement is true? a. The concordance rates indicate that only acute infection has a significant genetic component to variation in these traits. b. The concordance rates indicate that only handedness has a significant genetic component to variation in these traits. c. The concordance rates indicate there is significant genetic component to variation in these traits. d. The concordance rates indicate there is no significant genetic component to variation in these traits.
d
A small difference between concordance rates for a trait in dizygotic twins and monozygotic twins suggests that: a. variation due to genotype is about equally as important as that due to environment. b. variation due to genotype is far more important than variation due to environment. c. the trait is probably due to a single gene that shows Mendelian inheritance patterns. d. the genes affecting the trait interact strongly with the environment. e. variation due to genotype is far less important than variation due to environment.
e
In twin studies, scientists measure concordance, which is defined as the: a. extent to which differences in the environment influences differences in phenotype. b. percentage of cases in which both members of a pair of fraternal twins, but not identical twins, show the trait when at least one member shows it. c. percentage of cases in which both members of a pair of identical twins, but not fraternal twins, show the trait when at least one member shows it. d. extent to which variation in phenotype in a population is due to variation in genotype. e. percentage of cases in which both members of a pair of twins show the trait when at least one member shows the trait.
e
Sometimes a fertilized egg, after a few of rounds of division, separates into two embryos that results in identical, or _____, twins. a. paternal b. maternal c. dizygotic d. fraternal e. monozygotic
e
In a study of concordance, a sample of identical twins was evaluated for adult-onset diabetes. The following data were collected for this trait: (1) in 36 identical twin pairs, both showed adult-onset diabetes. (2) in 40 identical twin pairs, only one showed adult-onset diabetes. (3) in 336 identical twin pairs, neither showed adult-onset diabetes. The data given in (1) and (2) can be used to calculate concordance for identical twins as follows: 36/(36 + 40) x 100 = 47%. true false
true
Twin studies have been used to assess the relative importance of "nature" versus "nurture" in determining variation among individuals for complex traits. Based on the findings of these studies, which statement is true? a. Fraternal twins differ only because of environment. b. Identical twins differ because of genotype and environment. c. Studies of fraternal twins compensate for environmental influences that may be stronger for identical twins compared to fraternal twins. d. The concordance of fraternal twins is greater than that of identical twins for most complex traits. e. High concordance rates are the result of the shared genetic and environmental characteristics of identical twins.
e
Twins that arise from two different fertilized eggs and are called _____ twins. a. paternal b. maternal c. bizygotic d. monozygotic e. dizygotic
e
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. true false
false
In a study of concordance, a sample of identical twins was evaluated for adult-onset diabetes. The following data were collected for this trait: (1) In 36 identical twin pairs, both showed adult-onset diabetes. (2) In 40 identical twin pairs, only one showed adult-onset diabetes. (3) In 336 identical twin pairs, neither showed adult-onset diabetes. The data given in (3) shows that a majority of identical twins do not have the disease and gives us the most information with regard to concordance of the trait. true false
false
In a study of concordance, a sample of identical twins was evaluated for adult-onset diabetes. The following data were collected for this trait: (1) in 36 identical twin pairs, both showed adult-onset diabetes. (2) in 40 identical twin pairs, only one showed adult-onset diabetes. (3) in 336 identical twin pairs, neither showed adult-onset diabetes. The concordance for adult-onset diabetes among fraternal twins is 10%. Thus, this trait is not likely to have a strong genetic component. true false
false
Only by studying identical twins raised in separate environments can scientists uncover the role of genes versus environment in the development of a specific trait. Comparing the occurrence of the trait in identical versus fraternal twins yields little usable data. true false
false
Red coloration in wheat seeds is a complex trait influenced by three unlinked genes, each with two different alleles A and a; B and b; C and c. The Punnett square shown provides the results of a mating between two plants that are both heterozygous at all three loci. The intensity of the red color phenotype is influenced by only one of the gene products. true false
false
Similar to single gene traits, traits determined by multiple genes also show the expected 3:1 ratio of phenotypes in the progeny between two heterozygotes. true false
false
The concordance rates for four different traits among pairs of MZ and DZ twins were studied, giving the following results. Which trait suggests the environment has more influence than the genetic component? trait 1 trait 3 trait 4 trait 2
trait 2