Concepts of Genetics, 11th Edition Klug, Cummings, Spencer & Palladino -Test Bank

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Concepts of Genetics, 11th Edition Klug, Cummings, Spencer & Palladino -Test Bank

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Concepts of Genetics, 11th Edition Klug, Cummings, Spencer & Palladino -Test Bank

Chapter 4   Extensions of Mendelian Genetics

 

1) With incomplete dominance, a likely ratio resulting from a monohybrid cross would be ________.

  1. A) 3:3
  2. B) 1:2:2:4
  3. C) 1:2:1
  4. D) 9:3:3:1
  5. E) 3:1

Answer:  C

Section:  4.3

 

2) A situation in which there are more than two alternative forms of a given gene would be called ________.

  1. A) multiple alleles
  2. B) alternation of generations
  3. C) codominance
  4. D) incomplete dominance
  5. E) hemizygosity

Answer:  A

Section:  4.5

 

3) A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.

  1. A) codominance
  2. B) epistasis
  3. C) dominance
  4. D) recessiveness
  5. E) additive alleles

Answer:  B

Section:  4.8

 

4) Typical ratios resulting from epistatic interactions in dihybrid crosses would be ________.

  1. A) 9:3:3:1, 1:2:1
  2. B) 1:1:1:1, 1:4:6:4:1
  3. C) 9:3:4, 9:7
  4. D) 1:2:2:4:1:2:1:2:1
  5. E) 3:1, 1:1

Answer:  C

Section:  4.8

 

 

5) With which of the following would hemizygosity most likely be associated?

  1. A) codominance
  2. B) incomplete dominance
  3. C) trihybrid crosses
  4. D) X-linked inheritance
  5. E) sex-limited inheritance

Answer:  D

Section:  4.11

6) A mutation in a gene often results in a reduction of the product of that gene. The term for this type of mutation is ________.

  1. A) codominance
  2. B) incomplete dominance
  3. C) gain of function
  4. D) multiple allelism
  5. E) loss of function or null (in the case of complete loss)

Answer:  E

Section:  4.1

 

7) Because of the mechanism of sex determination, males of many species can be neither homozygous nor heterozygous. Such males are said to be ________.

  1. A) dominant
  2. B) hemizygous
  3. C) recessive
  4. D) complementary
  5. E) None of the answers listed is correct.

Answer:  B

Section:  4.11

 

8) Assume that a dihybrid cross (AaBb AaBb) is made in which the gene loci are autosomal, independently assorting, and incompletely dominant. What phenotypic ratio would you expect from such a cross? Just provide the ratio, not the phenotypes.

Answer:  1:2:1:2:4:2:1:2:1

Section:  4.3

 

9) Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white, aaBB or aaBb gives yellow, and aabb produces green. Assume that two fully heterozygous plants are crossed. Give the phenotypes (with frequencies) of the offspring.

Answer:  12 (white):3 (yellow):1 (green)

Section:  4.8

 

 

10) In mice, there is a set of multiple alleles of a gene for coat color. Four of those alleles are as follows:

 

C         = full color (wild)

cch       = chinchilla

cd        = dilution

c          = albino

 

Given that the gene locus is not sex-linked and that each allele is dominant to those lower in the list, diagram the crosses indicated below and give the phenotypic ratios expected from each.

 

(a) wild (heterozygous for dilution) chinchilla (heterozygous for albino)

(b) chinchilla (heterozygous for albino) albino

Answer:

(a)        Ccd  cchc  2 full color:1 chinchilla:1 dilution

(b)        cchc  cc 1 chinchilla:1 albino

Section:  4.5

11) A mutant gene that produces brown eyes (bw) is located on chromosome #2 of Drosophila melanogaster, whereas a mutant gene producing bright red eyes, scarlet (st), is located on chromosome #3. Phenotypically, wild-type flies (with dull red eyes), whose mothers had brown eyes and whose fathers had scarlet eyes, were mated. The 800 offspring possessed the following phenotypes: wild type (dull red), white, scarlet (bright red), and brown. Most of the 800 offspring had wild-type eyes, whereas those with white eyes were the least frequent.

 

(a) Using standard symbolism, diagram the cross from the P generation (brown-eyed mothers scarlet-eyed fathers) and the F1 generation. Be certain to provide the alleles of the mutant genes.

(b) From the information presented above, how many white-eyed flies would you expect in the F2 generation?

Answer:

(a)  P     bw/bw; st+/st+               bw+/bw+; st/st

F1:  bw+/bw; st+/st               bw+/bw; st+/st

 

(b) 50

Section:  4.8

 

 

12) In the mouse, gene A allows pigmentation to be deposited in the individual coat hairs; its allele a prevents such deposition of pigment, resulting in an albino. Gene B gives agouti (wild-type fur); its allele b gives black fur.

 

(a) Diagram the cross between a doubly heterozygous agouti mouse mated with a doubly homozygous recessive white mouse.

(b) What would be the expected phenotypic ratio in the progeny?

Answer:

(a)        AaBb aabb

(b)        1 (agouti):1 (black):2 (albino)

Section:  4.8

 

13) The trait of medium-sized leaves in iris is determined by the genetic condition PP. Plants with large leaves are PP, whereas plants with small leaves are PP. A cross is made between two plants each with medium-sized leaves. If they produce 80 seedlings, what would be the expected phenotypes, and in what numbers would they be expected? What is the term for this allelic relationship?

Answer:  20 (large leaves), 40 (medium leaves), 20 (small leaves); incomplete dominance

Section:  4.4

14) The trait for medium-sized leaves in iris is determined by the genetic condition PP. Plants with large leaves are PP, whereas plants with small leaves are PP. The trait for red flowers is controlled by the genes RR, pink by RR, and white by RR. A cross is made between two plants each with medium-sized leaves and pink flowers. If they produce 320 seedlings, what would be the expected phenotypes, and in what numbers would they be expected? Assume no linkage.

Answer:

20 large, red

40 medium, red

20 small, red

40 large, pink

80 medium, pink

40 small, pink

20 large, white

40 medium, white

20 small, white

Section:  4.4

 

 

15) The following coat colors are known to be determined by alleles at one locus in horses:

 

palomino = golden coat with lighter mane and tail

cremello = almost white

chestnut = brown

 

The following table gives ratios obtained in matings of the above varieties:

 

Cross             Parents                     Offspring

 

1          cremello cremello            all cremello

2          chestnut chestnut            all chestnut

3          cremello chestnut            all palomino

4          palomino palomino         1/4 = chestnut

1/2 = palomino

1/4 = cremello

 

Assign gene symbols for the genetic control of coat color on the basis of these data.

Diagram the last two matings.

Answer:  C1C1 = cremello, C2C2 = chestnut, C1C2 = palomino

(3)        C1C1  C2C2

(4)         C1C2  C1C2

Section:  4.5

 

16) What is meant by the term epistasis? Distinguish between epistasis and dominance. Do not use examples in answering this question.

Answer:  Epistasis refers to a gene (or genes) of one pair masking the expression of a gene (or genes) at a different locus. Dominance refers to the form of expression of a gene in relation to its allele (or alleles). When an allele is dominant, the heterozygous combination is the same phenotypically as one of the homozygotes. Epistasis is a nonallelic interaction; dominance is an allelic interaction.

Section:  4.8

17) The following F2 results occur from a typical dihybrid cross:

 

purple:       A_B_         9/16

white:        aaB_         3/16

white:        A_bb         3/16

white:        aabb          1/16

 

If a double heterozygote (AaBb) is crossed with a fully recessive organism (aabb), what phenotypic ratio is expected in the offspring?

Answer:  3 (white):1 (purple)

Section:  4.8

 

 

18) Which types of ratios are likely to occur in crosses (F2) when one is dealing with two interacting, epistatic gene pairs?

Answer:  9:7, 9:3:4, 12:3:1, 15:1

Section:  4.8

 

19) Assume that a cross is made between two organisms that are both heterozygous for a gene that shows incomplete dominance. What phenotypic and genotypic ratios are expected in the offspring?

Answer:  1:2:1

Section:  4.3

 

20) Assume that a dihybrid cross is made in which the genes loci are autosomal, independently assorting, and incompletely dominant. How many different phenotypes are expected in the offspring?

Answer:  9

Section:  4.3

 

21) How many different alleles can a gene have?

Answer:  Theoretically, an extremely large number of possibilities exist. Various bases could change, giving a variety of alleles, and combinations of those changed bases could provide additional variety.

Section:  4.1

 

22) Assume that a dihybrid F2 ratio, resulting from epistasis, was 9:3:4. If a double heterozygote was crossed with the fully recessive type, what phenotypic ratio is expected among the offspring?

Answer:  1:1:2

Section:  4.8

 

23) Assume that a dihybrid F2 ratio, resulting from epistasis, was 15:1. If a double heterozygote was crossed with the fully recessive type, what phenotypic ratio is expected among the offspring?

Answer:  3:1

Section:  4.8

 

24) Name four modes of inheritance that are influenced by the sex of individuals.

Answer:  X-linked, sex-influenced, sex-limited, Y-linked

Section:  4.11, 4.12

25) The white-eye gene in Drosophila is recessive and sex-linked. Assume that a white-eyed female is mated to a wild-type male. What would be the phenotypes of the offspring?

Answer:  females wild type, males white eyed

Section:  4.11

 

 

26) Two forms of hemophilia are determined by genes on the X chromosome in humans. Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man. What is the probability that their first son will have hemophilia?

Answer:  1/2

Section:  4.11

 

27) Two forms of hemophilia are determined by genes on the X chromosome in humans. Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man. What is the probability that their first daughter will have hemophilia?

Answer:  0

Section:  4.11

 

28) State a significant difference between X-linked and sex-influenced inheritance.

Answer:  In X-linked inheritance, the gene in question is on the X chromosome; in sex-influenced inheritance, the gene is autosomal.

Section:  4.11, 4.12

 

29) Pattern baldness is determined by a single autosomal gene pair. When females are homozygous for this gene pair, can they show pattern baldness?

Answer:  Yes, but the phenotype is less pronounced and is expressed later in life.

Section:  4.12

 

30) Provide an example of sex-influenced inheritance.

Answer:  pattern baldness in humans, horn formation in sheep, certain coat patterns in sheep

Section:  4.13

 

31) What distinguishes sex-limited from sex-influenced inheritance?

Answer:  In sex-limited inheritance, expression is limited to one sex; in sex-influenced inheritance, expression differs between the sexes.

Section:  4.12

 

32) Comb shape in chickens represents one of the classic examples of gene interaction. Two gene pairs interact to influence the shape of the comb. The genes for rose comb (R) and pea comb (P) together produce walnut comb. The fully homozygous recessive condition (rrpp) produces the single comb. Assume that a rose-comb chicken is crossed with a walnut-comb chicken and the following offspring are produced: 17 walnut, 16 rose, 7 pea, 6 single.

 

(a) What are the probable genotypes of the parents?

(b) Give the genotypes of each of the offspring classes.

Answer:

(a)        Rrpp RrPp

 

(b) R_Pp   (walnut)

      R_pp    (rose)

      rrPp     (pea)

      rrpp     (single)

Section:  4.8

33) Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white, aaBB or aaBb gives yellow, and aabb produces green. Crosses among heterozygotes give a 12:3:1 ratio. What type of gene interaction would account for these results?

Answer:  epistasis

Section:  4.8

 

34) A particular cross gives a modified dihybrid ratio of 9:7. What phenotypic ratio would you expect in a testcross of the fully heterozygous F1 crossed with the fully recessive type? Diagram the testcross using A,a,B,b as symbol sets.

Answer:  1:3   AaBb aabb > AaBb, Aabb, aaBb, aabb

Section:  4.8

 

35) The enzyme glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as a recessive gene on the X chromosome in humans. A phenotypically normal woman (whose father had G6PD) is married to a normal man.

 

(a) What fraction of their sons would be expected to have G6PD?

(b) If the husband had G6PD, would it make a difference in your answer in part (a)?

Answer:

(a) 1/2

(b) no

Section:  4.11

 

36) A cross was made between homozygous wild-type female Drosophila and yellow-bodied male Drosophila. All of the resulting offspring were phenotypically wild type. Offspring of the F2 generation had the following phenotypes:

 

Sex                  Phenotype       Number

 

male                wild                   96

male                yellow                99

female             wild                 197

 

Based on this information:

(a) Is the mutant gene for yellow body behaving as a recessive or dominant?

(b) Is the yellow locus on an autosome or on the X-chromosome?

Answer:

(a) recessive

(b) X-chromosome

Section:  4.11

 

37) Below is a pedigree of a fairly common human hereditary trait in which the boxes represent males and the circles represent females. Shading symbolizes the abnormal phenotype.

 

Given that one gene pair is involved:

(a) Is the inheritance pattern X-linked or autosomal, recessive or dominant?

(b) Give the genotype of each individual in the pedigree. If more than one genotypic possibility exists, present all possible alternatives.

 

 

Answer:

(a) autosomal recessive

 

(b)

 

Section:  4.11

 

38) The genes for zeste eyes and forked bristles are located on the X chromosome in Drosophila melanogaster. Both genes are recessive. A cross is made between a zeste-eyed female and a forked-bristled male.

 

(a) If 200 offspring from this cross were obtained, present the expected number, sex, genotype, and phenotype in each class of the F1.

(b) If the F1 offspring were crossed to produce 800 flies of an F2 generation, present the expected number, sex, and phenotype in each class. Assume no crossing over.

Answer:

(a)        z+f/z f+      =          wild female     (100)

            z f+/Y        =          zeste male        (100)

 

(b)        z+f/z f+      =          wild female     (200)

            z f+/z f+     =          zeste female    (200)

            z+f/Y         =          forked male     (200)

            z f+/Y        =          zeste male        (200)

Section:  4.11

 

 

39) In a mating between individuals with the genotypes IAi  ii, what percentage of the offspring would be expected to have the O blood type?

Answer:  50%

Section:  4.5

40) In a mating between individuals with the genotypes IAIB  ii, what percentage of the offspring would be expected to have the O blood type?

Answer:  zero

Section:  4.5

 

41) If an X-linked disorder is lethal to the affected individual prior to the age at which one reaches reproductive maturation, the lethality will be expressed only in males. Why is this so?

Answer:  The only sources of the lethal allele in the population are heterozygous females who are carriers and do not express the disorder.

Section:  4.6, 4.11

 

42) Can females display pattern baldness?

Answer:  When females inherit the BB genotype, they can definitely express hair thinning; however, it is less pronounced than in males and occurs later in life.

Section:  4.12

 

43) Regarding the ABO blood group system in humans, if an individual is genetically IBi and yet expresses the O blood type, which genotype is it likely to have?

Answer:  hh (Bombay)

Section:  4.5, 4.8

 

44) With multiple alleles, there can be more than two genetic alternatives for a given locus.

Answer:  TRUE

Section:  4.5

 

45) With both incomplete dominance and codominance, one expects heterozygous and homozygous classes to be phenotypically identical.

Answer:  FALSE

Section:  4.3, 4.4

 

46) The ABO blood group locus in humans provides an example of epistasis.

Answer:  FALSE

Section:  4.5

 

47) Sex-limited inheritance is the same as sex-linked inheritance.

Answer:  FALSE

Section:  4.11, 4.12

 

48) A conditional mutant is one whose expression is influenced by some environmental condition.

Answer:  TRUE

Section:  4.13

49) A typical epistatic ratio is 9:3:4.

Answer:  TRUE

Section:  4.8

 

50) A 9:7 ratio indicates incomplete dominance.

Answer:  FALSE

Section:  4.3

51) Pattern baldness and hen/cock feathering in fowl are examples of X-linked inheritance.

Answer:  FALSE

Section:  4.12

 

52) Penetrance specifically refers to the expression of lethal genes in heterozygotes.

Answer:  FALSE

Section:  4.13

 

53) Expressivity is the term used to describe the balanced genetic output from a hemizygous condition.

Answer:  FALSE

Section:  4.13

 

54) Hemizygosity is the term one uses to describe the state of a gene that has no allele on the opposing chromosome.

Answer:  TRUE

Section:  4.11

 

55) Genomic imprinting occurs when one allele converts another.

Answer:  FALSE

Section:  4.13

 

56) Genomic anticipation refers to observations that a genetic disorder occurs at an earlier age in successive generations, whereas genetic imprinting occurs when gene expression varies depending on parental origin.

Answer:  TRUE

Section:  4.13

 

57) Gain of function mutations are generally dominant since one copy in a diploid organism is sufficient to alter the normal phenotype.

Answer:  TRUE

Section:  4.1

 

58) Assume that a mutation occurs in the gene responsible for the production of hexosaminidase A, such that only about 50% of the enzyme activity is found in the heterozygote compared with a homozygous normal individual. If heterozygotes are phenotypically normal, we would say that the mutant allele is recessive to its normal allele.

Answer:  TRUE

Section:  4.1

59) Alleles that are masked by an epistatic locus are said to be hypostatic to the genes at that locus.

Answer:  TRUE

Section:  4.8

 

60) One result of X-linkage is a crisscross pattern of inheritance in which sons express recessive genes of their fathers and daughters express recessive genes of their mothers.

Answer:  FALSE

Section:  4.12

61) The term expressivity defines the percentage of individuals who show at least some degree of expression of a mutant genotype.

Answer:  FALSE

Section:  4.13

 

Chapter 16   Regulation of Gene Expression in Prokaryotes

 

1) Which term refers to a contiguous genetic complex that is under coordinate control?

  1. A) lysogen
  2. B) prototroph
  3. C) operon
  4. D) allosteric
  5. E) attenuation

Answer:  C

Section:  16.2

 

2) Genetic regulation in eukaryotes can take place at a variety of levels from transcriptional to posttranslational. At which level is genetic regulation considered most likely in prokaryotes?

  1. A) transcriptional
  2. B) capping
  3. C) polyadenylation of the 3 end of the mRNAs
  4. D) intron processing
  5. E) exon processing

Answer:  A

Section:  16.1, 16.2

 

3) Which term would be applied to a regulatory condition that occurs when protein greatly reduces transcription when associated with a particular section of DNA?

  1. A) negative control
  2. B) positive control
  3. C) inhibition
  4. D) activation
  5. E) stimulation

Answer:  A

Section:  16.1

 

4) Which term most appropriately refers to a regulatory protein in prokaryotes?

  1. A) translation
  2. B) RNA processing
  3. C) DNA binding protein
  4. D) gyrase action
  5. E) helicase activation

Answer:  C

Section:  16.1, 16.2, 16.4

 

 

5) In the lactose operon, the product of structural gene lacZ is capable of ________.

  1. A) nonautonomous replication
  2. B) forming lactose from two glucose molecules
  3. C) replacing hexokinase in the early steps of glycolysis
  4. D) splitting the -linkage of lactose
  5. E) forming ATP from pyruvate

Answer:  D

Section:  16.2

6) Which of the following terms best characterizes catabolite repression associated with the lactose operon in E. coli?

  1. A) inducible system
  2. B) repressible system
  3. C) negative control
  4. D) positive control
  5. E) constitutive

Answer:  D

Section:  16.3

 

7) When referring to attenuation in regulation of the tryptophan operon, it would be safe to say that when high levels of tryptophan are available to the organism, ________.

  1. A) the tryptophan operon is being transcribed at relatively high levels
  2. B) translational termination is likely
  3. C) transcriptional termination is likely
  4. D) tryptophan is inactivating the repressor protein
  5. E) ribosomes are stalling during translation of the attenuator region

Answer:  C

Section:  16.6

 

8) Under the system of genetic control of the tryptophan operon, ________.

  1. A) when there are high levels of tryptophan in the medium, transcription of the trp operon occurs at high levels
  2. B) when there is no tryptophan in the medium, transcription of the trp operon occurs at high levels
  3. C) when there are high levels of tryptophan in the medium, transcription of CAP (CRP) occurs at high levels
  4. D) when there are high levels of tryptophan in the medium, ribosomes stall and reduce the levels of tryptophan synthesized
  5. E) no transcription occurs under any nutritional circumstance because negative controls inhibit transcription

Answer:  B

Section:  16.5

 

 

9) This question relates to the regulation of enzymes involved in the synthesis of tryptophan in E. coli. If tryptophan is present in the medium and available to the bacterium, ________.

  1. A) the repressor is inactive and the tryptophan operon is off
  2. B) the repressor is inactive and the tryptophan operon is on
  3. C) the repressor is bound to the operator, thus blocking transcription
  4. D) the five structural genes associated with tryptophan synthesis are being transcribed at induced levels
  5. E) positive control is occurring

Answer:  C

Section:  16.5

 

10) Certain mutations in the regulator gene of the lac system in E coli result in maximal synthesis of the Lac proteins (-galactosidase, etc.) even in the absence of the inducer (lactose). Provide an explanation for this observation.

Answer:  Either there has been a mutation in the gene that produces the repressor or the operator is mutated so that it will not interact with the repressor.

Section:  16.2

11) Describe in detail the actions of the regulatory proteins in inducible and repressible enzyme systems.

Answer:  Inducible system: The repressor is normally active, but the inducer inactivates the repressor. Repressible system: The repressor is normally inactive but is activated by the corepressor. Active repressors turn off transcription.

Section:  16.1, 16.2, 16.3

 

12) Compare and contrast positive and negative control of gene expression in bacteria.

Answer:  Both forms of control result from an interaction of a molecule (usually considered to be a protein) with the genetic material (either RNA or DNA). Positive control results when the interaction stimulates transcription, whereas negative control occurs when the interaction inhibits transcription.

Section:  16.1, 16.2, 16.3

 

 

13) (a) Describe, by labeled diagram, the structural components of the lactose operon in E. coli. (b) State the function of the lac regulator gene. (c) State the function of -galactosidase in the lac system. (d) Show, by diagram, the manner in which lactose brings about transcription of the three structural genes of the lac operon. (e) Explain why certain mutations in the regulator gene (I-) of the lac system result in maximal synthesis of -galactosidase, permease, and transacetylase even in the absence of the inducer (lactose).

Answer:

(a) See appropriate diagrams in the Klug et al. text.

(b) The regulator gene produces a repressor protein, which interacts with the operator to shut off

transcription. In the presence of lactose, the repressor protein does not interact with the

operator.

(c) -galactosidase cleaves the lactose sugar into its components glucose and galactose.

(d) See appropriate diagrams in the Klug et al. text.

(e) Such mutations provide modified proteins that are unable to associate with the operator to

shut off transcription.

Section:  16.2

14) The following table lists several genotypes associated with the lac operon in E. coli. For each, indicate with a + or a - whether -galactosidase would be expected to be produced at induced levels. (Assume that glucose is not present in the medium.)

 

-galactosidase production

Genotype                                                        No Lactose           On Lactose

 

(a)        I + O+ Z+/ F I O+ Z+

(b)        I Oc Z+/ FI O+ Z-

(c)        I s Oc Z+/ FI + O+ Z+

(d)       I O+ Z+/ F I O+ Z+

 

I+  = wild-type repressor

I-   = mutant repressor (unable to bind to the operator)

Is   = mutant repressor (insensitive to lactose)

O+      = wild-type operator

Oc = constitutive operator (insensitive to repressor)

Answer:

(a)                   +

(b)        +          +

(c)        +          +

(d)       +          +

Section:  16.2

 

 

15) The following table lists several genotypes associated with the lac operon in E. coli. For each, indicate with a + or a - whether active -galactosidase would be expected to be produced at induced levels. (Assume that glucose is not present in the medium.)

 

-galactosidase production

Genotype                                                        No Lactose           On Lactose

 

(a)        I + O+ Z+/ F I + O+ Z+

(b)        I Oc Z-/ F I Oc Z-

(c)        I Oc Z+/ F I O+ Z+

(d)       I s Oc Z-/ F I s O+ Z+

 

I +       = wild-type repressor

I-  = mutant repressor (unable to bind to the operator)

Is  = mutant repressor (insensitive to lactose)

O+       = wild-type operator

Oc       = constitutive operator (insensitive to repressor)

 

Answer:

(a)                   +

(b)                  

(c)        +          +

(d)                 

Section:  16.2

16) State whether the following statement is true or false; then give your reasoning. The terminating hairpin loop occurs in the tryptophan operon when sufficient tryptophan is present.

Answer:  True, the hairpin loop terminates transcription.

Section:  16.6

 

17) Describe what is meant by a gratuitous inducer. Give an example.

Answer:  A gratuitous inducer is a chemical analog of a natural inducer. It serves as an inducer but is not a substrate for the reactions related to the natural inducer. Isopropylthiogalactoside (IPTG) is a gratuitous inducer of the lactose operon.

Section:  16.2

 

18) Describe the positive control exerted by the catabolite activating protein (CAP). Include a description of catabolite repression.

Answer:  Regarding regulation of the lac operon, in the absence of glucose, CAP (dependent on cAMP and adenyl cyclase) binds to the CAP site and facilitates transcription (positive control). Transcription of the operon is inhibited in the presence of glucose (catabolite repression).

Section:  16.3

 

 

19) In terms of prokaryotic growth efficiency, discuss the relationship of availability of growth substances to the regulation of genetic pathways involved in synthesis of those substances.

Answer:  Genetic systems have evolved that allow for in-house production of growth substances when not supplied in the environment or when in full supply. When needed substances are in full supply, certain of these genetic systems are repressed.

Section:  16.1

 

20) Within the control region of the tryptophan operon is a section of DNA that is sensitive to levels of tryptophan in the system. What is the name of this region?

Answer:  leader or attenuator region

Section:  16.6

 

21) Given the following diagram, which type of control, positive or negative, is operating?

 

Answer:  positive

Section:  16.1

 

22) Regarding regulation of the tryptophan operon, which type of regulatory molecule might one appropriately call the amino acid tryptophan?

Answer:  corepressor

Section:  16.5

23) Mutations in the lacI and lacO genes in the lactose system often lead to full production of the three structural genes related to the lac operon even with no lactose available to the organism. Such mutations would be called ________.

Answer:  constitutive

Section:  16.2

 

24) Constitutive mutations may occur in various components of the lac operon. Name two types of constitutive mutations.

Answer:  lacI  and lacOc

Section:  16.2

 

25) What is the function of the lacY gene in the lactose operon?

Answer:  The lacY gene codes for -galactoside permease, a membrane-bound protein, which transports lactose into the bacterial cell.

Section:  16.2

 

 

26) Explain why lacOc mutations are cis-acting, whereas lacI mutations can be trans-acting.

Answer:  The operator region does not produce a diffusible product, whereas the lacI gene does.

Section:  16.2

 

27) Briefly describe the structure and abundance of the lac repressor protein.

Answer:  tetramer of identical units, with 5 to 10 tetramers present in each cell

Section:  16.2

 

28) What experimental results would indicate that the mutation lacIs is dominant to lacI+?

Answer:  In lacIs / lacI+ partial diploids, the lac operon is in a repressed state in the presence of lactose.

Section:  16.2

 

29) Monod discovered that if tryptophan is present in relatively high quantities in the growth medium, the enzymes necessary for its synthesis are repressed. How does this occur?

Answer:  Tryptophan acts as a corepressor to activate the tryptophan repressor protein; it is also involved in an attenuation system, which causes the termination of transcription.

Section:  16.5, 16.6

 

30) What is meant by polycistronic mRNA? Give an example.

Answer:  It is a messenger RNA polymer that carries the code for more than one polypeptide chain; lactose and tryptophan operons would be examples.

Section:  16.2

 

31) When considering the binding of cAMP-CAP and RNA polymerase to the lac operon, both bind more efficiently than either singly. Which term is applied to this increased efficiency of binding?

Answer:  cooperative binding

Section:  16.3

 

32) Describe an allosteric molecule.

Answer:  There is more than one binding site, and binding to that site can alter the structure of the protein.

Section:  16.2

33) Which symbols are used to describe constitutive mutations in the lac system?

Answer:  I- and Oc

Section:  16.2

 

34) Regarding the tryptophan operon, trpR- maps a considerable distance from the structural genes. The mutation either inhibits the interaction with tryptophan or inhibits repressor formation entirely. In the presence of tryptophan in the medium, would you expect the tryptophan operon to be transcriptionally active in this mutant? Explain.

Answer:  With either of the two scenarios mentioned in the problem, absence of repressor function in a repressible system means that there would be no repression of the operon. The operon would be transcriptionally active.

Section:  16.5

35) The catabolite repression system in E. coli essentially represses the lac operon when glucose is present. What evolutionary advantage would favor such a system?

Answer:  Glucose can enter glycolysis as is, whereas lactose must first be split into glucose and galactose. To do so, the energy-requiring synthesis of -galactosidase is needed. It is energy efficient to burn glucose rather than lactose.

Section:  16.3

 

36) The lac operon consists of three structural genes as well as the adjacent region of DNA known as the regulator.

Answer:  FALSE

Section:  16.2

 

37) Regarding the lactose utilization system in E. coli, a constitutive mutant is one in which the three enzymes are produced regardless of the presence or absence of lactose.

Answer:  TRUE

Section:  16.2

 

38) Regarding the lactose utilization system in E. coli, a gratuitous inducer is a molecule that is chemically analogous to lactose and induces the operon but is not a substrate for the enzymes of the lac operon.

Answer:  TRUE

Section:  16.2

 

39) Under a system of negative control, genetic expression occurs unless such expression is shut off by some form of regulator.

Answer:  TRUE

Section:  16.1

 

40) Under a system of positive control, transcription does not occur unless a regulator molecule directly stimulates RNA production.

Answer:  TRUE

Section:  16.1

 

41) The enzyme -galactoside permease cleaves the linkage between glucose and galactose in lactose.

Answer:  FALSE

Section:  16.2

42) The tryptophan operon is typically characterized by the following two terms: negative control and repressible.

Answer:  TRUE

Section:  16.5

 

43) Attenuation is known to occur in the lactose operon.

Answer:  FALSE

Section:  16.6

 

44) Attenuation involves the termination of mRNA synthesis.

Answer:  TRUE

Section:  16.6

 

45) Both the tryptophan and lactose operons include forms of control that are typically called negative.

Answer:  TRUE

Section:  16.1, 16.2, 16.5

 

Chapter 24   Genetics of Behavior

 

1) Autism spectrum disorders are neurodevelopmental disorders that appear to be ________.

  1. A) caused by a single dominant gene
  2. B) multifactorial and complex in nature with a genetic component
  3. C) caused by several genes located on the X chromosome
  4. D) caused by a low number of recessive genes located mainly on the autosomes
  5. E) directly related to trinucleotide repeat increases but not decreases

Answer:  B

Section:  24.3

 

2) Recent research using gene expression profiles indicates that schizophrenia and autism spectrum disorders are ________.

  1. A) like opposite sides of the same coin
  2. B) identical at the molecular level
  3. C) completely unrelated
  4. D) likely to be caused by the same dominant gene
  5. E) likely to be caused by the same recessive gene

Answer:  A

Section:  24.3

 

3) What conclusion has been reached regarding the genetic status of schizophrenia using genome-wide association studies?

  1. A) A single dominant gene is involved.
  2. B) No single gene or allele makes a significant contribution.
  3. C) A single recessive gene is involved.
  4. D) Several dominant genes located on the X chromosome cause this disease.
  5. E) No more than three loci are involved in the expression of schizophrenia.

Answer:  B

Section:  24.3

 

4) What is a major problem that arises in the study of the genetic basis of human behavior?

  1. A) Memories of individuals are unreliable.
  2. B) People are too short lived.
  3. C) Behaviors are difficult to define objectively.
  4. D) The environment plays no role in behavioral expression.
  5. E) The environment is the only factor that determines human behavior.

Answer:  C

Section:  24.3

 

5) One of the oldest recorded behavior mutants is the waltzer mutation in the mouse. Mutant mice can be observed dancing and head shaking; some are also deaf. Mice must be homozygous for a mutation to express the trait. Based on this information, the genetic cause of this trait is most likely a(n) ________.

  1. A) simple recessive pattern of inheritance
  2. B) multifactor, polygenic pattern of inheritance
  3. C) dominant/recessive pattern typical of other behavioral traits
  4. D) epistatic pattern with incomplete dominance
  5. E) variable gene activity pattern with overdominance causing deafness

Answer:  A

Section:  24.1

 

6) Humans are relatively unavailable as experimental subjects in genetic investigations, yet considerable interest surrounds intelligence, language, personality, and emotional behaviors. One difficulty in studying such behaviors is the high likelihood that they ________.

  1. A) are strongly influenced by birth order and diet
  2. B) are affected by the environment
  3. C) follow non-Mendelian patterns of inheritance
  4. D) follow extranuclear patterns of inheritance
  5. E) have no likely genetic influence

Answer:  B

Section:  24.3

 

7) Huntington disease (HD) is a well-studied, autosomal dominant disorder that affects the nervous system. Symptoms usually appear after age 40, and victims usually die within 10 to 15 years after onset of the disease. It appears that at least in some cases of HD, stutter mutations occur. Such mutations are characterized by ________.

  1. A) uncontrolled verbal capacity of patients
  2. B) extra trinucleotide repeats within the HD gene
  3. C) RNA polymerase imperfections leading to altered DNAs
  4. D) repeated DNA polymerases generating too many coding symbols
  5. E) links between monoamine oxidase A (MAOA) and hexokinase

Answer:  B

Section:  24.3

 

8) Present an overview of the research dealing with the genetics of behavior in small mammals (mice or rats) and Drosophila.

Answer:  mice or rats: fear and anxiety, Huntington disease; Drosophila: geo- and phototaxis and single gene influences such as those relating to courtship and mating, learning and memory

Section:  24.1, 24.2

 

9) Much effort has been expended to understand genetic involvement in brain function in Drosophila. Why might this research be important in understanding the functioning of the human brain?

Answer:  Mammalian homologs of the Drosophila genes are active in parts of mammalian brains.

Section:  24.2

10) How would the use of a large series of monozygotic and dizygotic twins enhance studies on the genetic basis of human behavior?

Answer:  Monozygotic twins are genetically identical, and when reared under the same versus different environments, one can estimate the degree to which variation in behavior is determined by heredity. Dizygotic twins are genetically different, but by having the same intrauterine and developing environment (if being reared in the same household), one can again estimate the influence of heredity on behavioral traits.

Section:  24.3

 

11) Why is cyclic AMP considered important in behavioral studies?

Answer:  Cyclic AMP affects short-term memory using the potassium channel in the plasma membrane and affects long-term memory by regulating the transcription factor CREB.

Section:  34.2

 

12) Describe what is meant by the nature-nurture controversy.

Answer:  Among complex organisms, it is often difficult to determine the roles of the environment and genes in determining certain traits, especially behavioral traits.

Section:  Introduction

 

13) Describe three general approaches used in the study of the genetics of behavior.

Answer:  determination of behavioral differences between genetic strains of closely related organisms, selection of strains, study of single gene effects

Section:  24.1, 24.2

 

14) Some behavioral studies have been carried out on E. coli, a bacterium. In what way might we learn about the complex behaviors of higher organisms by a study of behavior in E. coli?

Answer:  Certain behaviors, such as chemotactic responses in E. coli, involve a number of gene products that process stimuli and generate responses through metabolic networks that involve protein phosphorylation. Such studies represent the most well-studied relationship between behavior and metabolism.

Section:  24.2

 

15) List at least three areas of research that deal with the genetics of behavior in humans.

Answer:  Huntington disease, schizophrenia, autism

Section:  24.3

 

16) The movement of a free-living organism toward or away from the source of an external stimulus is called ________.

Answer:  taxis

Section:  24.1

 

17) List two problems with determining the genetic basis of a behavioral trait in humans.

Answer:  influence of the environment and difficulty in conducting genetic studies on humans

Section:  24.3

 

18) Determining the genetic influence on two fairly common human behavioral disorders has eluded researchers for many years. One involves passive deficits in thinking, language, feelings, and social skills; the other includes a variety of psychotic symptoms, perceptual disorders (hearing voices), and withdrawal from reality. Evidence from pedigrees and twins indicates that these two behaviors have a genetic component. Which behaviors are being described here?

Answer:  autism and schizophrenia

Section:  24.3

 

19) The HD gene, one of the first genes to be mapped in humans by RFLP, is located on the short arm of chromosome 4. It codes for ________.

Answer:  a large protein (350 kd) called huntingtin

Section:  24.3

 

20) Briefly describe the mutant status of the HD gene.

Answer:  The HD gene encodes a 350 kd protein (huntingtin) in which mutant alleles have extra CAG trinucleotide repeats near the 5 end. Normal individuals have 7 to 34 repeats, whereas those with HD carry more than 40 repeats.

Section:  24.3

 

21) The symptoms of Huntington disease usually appear in the fifth decade of life in humans

Answer:  TRUE

Section:  24.3

 

22) A transgenic mouse model now exists for Huntington disease in humans.

Answer:  TRUE

Section:  24.3

 

23) In studies attempting to determine a genetic basis for a given behavior, if the environment is held constant, and behavioral differences directly correlate with genetic differences, a genetic basis for the behavioral state is supported.

Answer:  TRUE

Section:  24.1, 24.2

 

24) The nature-nurture controversy exists as a result of the difficulty in assessing the roles of environment and genes in the determination of certain traits, especially behavioral traits.

Answer:  TRUE

Section:  Introduction

 

25) Evidence from genome-wide association studies on schizophrenia indicates that no single gene or allele makes a significant contribution to this disorder.

Answer:  TRUE

Section:  24.3

 

26) The availability of a large series of monozygotic and dizygotic twins often enhances studies on the genetic basis of human behavior.

Answer:  TRUE

Section:  24.3

27) Drosophila have too much variation in their geotactic patterns to be useful in the study of the genetic basis of behavior.

Answer:  FALSE

Section:  24.1

 

28) Geotaxis in Drosophila appears to be dependent on a single-locus genetic system.

Answer:  FALSE

Section:  24.1

 

29) Mitochondrial ribosomes are responsible for determining the geotactic response in Drosophila.

Answer:  FALSE

Section:  24.2

 

30) Drosophila can learn and remember.

Answer:  TRUE

Section:  24.1

 

31) Individuals with Huntington disease have a point mutation in a gene coding for the p53 protein.

Answer:  FALSE

Section:  24.3

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