Genetics: Exam 3

In a cross between two true-breeding parents that both exhibit the dominant phenotype, ___ percent of the offspring will exhibit the recessive phenotype. 0 25 50 100

0

In a pea plant that is heterozygous for seed color, what proportion of gametes will carry the recessive allele? 1/4 3/4 all of the gametes will carry the recessive allele 1/8 1/2

1/2

In lilies, white flowers (W) are dominant to purple flowers (w). If two plants that are heterozygous for flower color are mated, the genotypic ratio of the offspring would be 1:1:1:1. 9:3:3:1. 1:2:1. 3:1. 1:1.

1:2:1

In his monohybrid crosses for seed color in peas, Mendel reported 6,022 yellow seeds and 2,001 green seeds. How many of each color class were expected? All should be green All should be yellow 4,011 green and 4,011 yellow 6,017 yellow and 2,006 green 2,006 yellow and 6,017 green

6,017 yellow and 2,006 green

In the F2 generation, how many genotypic classes could be generated from a dihybrid cross of two heterozygotes in which the genes involved show complete dominance? 9 12 8 3 4

9

The protein class(es) involved in the activation of transcription is (are) transactivators. general transcription factors (GTFs). coactivators. A and B only A, B, and C

A, B, and C

Which of the following secondary structures may be a DNA-binding domain? Leucine zipper Zinc finger Helix-turn-helix A and B only A, B, and C

A, B, and C

Which of the following genotypes would not usually be represented in a gamete? AA Ab AB aB ab

AA

Gene expression in eukaryotes is regulated at the level of transcription. RNA processing. translation. All of the listed responses are correct.

All of the listed responses are correct.

Control of transcription initiation of eukaryotic protein-coding genes involves repressors. activators. enhancers. promoters. All of these

All of these

A diploid plant has two different alleles of a flower color gene (genotype Rr). Which diagram best shows where the two alleles would be found on the plant's chromosomes?

Answer is A located in same spot for R and r

Genomic imprinting A) Bind to the 3' UTR of target RNAs B) Processed by Ago2, targets only one RNA C) Gene regulation dependent on parent of origin D) DNA element bound by activators E) Proteins recruited by activators

C) Gene regulation dependent on parent of origin

A constitutive gene is a gene that is occasionally expressed. True False

False

A testcross with a heterozygous dominant individual will yield only heterozygous dominant offspring. True False

False

Eukaryotic repression generally occurs via physical blockage of the promoter. True False

False

Genes required for maintaining basic cell structure, growth, and division are housekeeping genes and have regulated expression. True False

False

Mutations of lacOC lead to attenuated expression of lac structural genes. True False

False

Recombinases mediate transcript processing from pre-mRNA to mature mRNA. True False

False

The enzyme transacetylase is responsible for uptake of lactose. True False

False

The genotypic F2 ratio expected in a dihybrid cross is 9:3:3:1. True False

False

If a protein has a zinc finger, leucine zipper, or helix-turn-helix sequence, what is likely function of this protein? It is a steroid hormone receptor. It is a transcriptional activator. It is a transcriptional repressor. It is a DNA-binding protein.

It is a DNA-binding protein

With respect to genetics, URS stands for upstream repressor-binding sequence. unregulated repression series. uracil response system. uniform response system. upstream regulatory sequence.

LOOK THIS UP

Which of the following mutations is dominant over wild-type lacI+ in a partial diploid experimental cell? lacO- lacIS lacA- lacI- C and Donly

LacIS

Gene silencing in eukaryotes is often achieved through chromatin structure. True False

True

Lactose is an inducer of the lac operon. True False

True

Mutants that are lacIS do not produce lac enzymes, regardless of the presence or absence of lactose. True False

True

The 3:1 phenotypic ratio observed among progeny of an F1 X F1 cross requires random union of gametes. True False

True

The placement of the operator sequence between the promotor and the structural genes is critical to the proper function of the lac operon. True False

True

The structural genes in the lac operon are transcribed into a single polycistronic mRNA molecule. True False

True

The use of CAP- cAMP complex as a positive regulator is specific to the lac operon. True False

True

Transcriptionally active genes show lower levels of DNA methylation compared with transcriptionally inactive genes. True False

True

True-breeding individuals are produced by repeated backcrossing. True False

True

Two individuals can be phenotypically identical, yet have different genotypes for a given trait. True False

True

lacIS encodes superrepressors, repressors that always bind to the operator and prevent gene transcription. True False

True

For any given gene, the principle of segregation predicts that each gamete produced as a result of meiosis will contain both alleles of a gene pair. a single allele of a gene pair. half of one allele of a gene pair. half of both alleles of the gene pair.

a single allele of a gene pair.

An enhancer element is a specific nucleotide sequence in DNA. a regulatory protein. an mRNA-degrading enzyme. an mRNA transcript.

a specific nucleotide sequence in DNA

2. When a promoter element is bound by a positive regulatory protein, the result is a) activation of transcription. b) activation of translation. c) repression of replication. d) repression of transcription.

a) activation of transcription.

Of the methods listed below, which would be the best way to determine which of two alleles of a gene is dominant to the other? a. Observe the relevant phenotype in the progeny that result from a cross between individuals from two different pure-breeding lines. b. Count the number of recessive individuals resulting from a cross between two recessive parents. c. Perform crosses between series of randomly selected pairs to see which phenotype occurs more frequently. d. Observe the relevant phenotype among the progeny of several crosses between individuals within a single, pure-breeding line.

a. Observe the relevant phenotype in the progeny that result from a cross between individuals from two different pure-breeding lines.

Unlike prokaryotes, most gene regulation in eukaryotes a. is controlled at the level of transcript processing. b. is based on posttranslational modification. c. takes place at the transcriptional level. d. is controlled by inhibitory proteins. e. None of these

a. is controlled at the level of transcript processing.

The half-life of a protein is directly related to a. its N-terminal amino acid residue. b. whether it is encoded by a constitutively expressed gene. c. the number of stabilizing cross-linkages. d. what kind of cell it is produced in. its tertiary structure.

a. its N-terminal amino acid residue.

When a promoter element is bound by a positive regulatory protein, the result is activation of transcription. activation of replication. repression of replication. activation of translation. repression of transcription

activation of transcription

Activators in eukaryotes bind to enhancers. may act as heterodimers with a DNA binding subunit and an activation subunit. may act as monomers may act as homodimers. All of these

all of these

Chromosome-level gene repression involves physical blockage of gene regions. supercoiling. nucleosomes. chromatin formation. All of these

all of these

RNA silencing involves miRNAs. a protein called Dicer. siRNAs. double-stranded RNA. All of these

all of these

mRNA regulation can be achieved at the level of translation. transport. life span (degradation). processing. All of these

all of these

The inducer of the lac operon is allolactose. glucose. repressor protein. permease. galactose.

allolactose

The interaction between allolactose and the repressor protein results in a shape change known as a(n) allosteric shift. transformant. isomer. enantiomer. mutation.

allosteric shift

Unlike bacterial operons, eukaryotic operons are exceedingly rare. are all negatively controlled. are all positively controlled. are restricted to certain eukaryotic kingdoms. None of these

are exceedingly rare

. If you are following 6 independently segregating traits and you cross two individuals heterozygous for all 6 of the traits. What is your expected number for genotypic classes and phenotypic classes, respectively? a) 729 phenotypes, 64 genotypes b) 729 genotypes, 64 phenotypes c) 216 phenotypes, 36 genotypes d) 216 genotypes, 36 phenotypes

b) 729 genotypes, 64 phenotypes

A true-breeding, or homozygous, brown mouse (male) is crossed with a true-breeding white mouse (female). All of the mice in the next F1 generation are brown, both males and females. These brown mice are interbred to produce an additional F2 generation, which consists of 12 brown mice and 4 white mice. If a single gene controls fur color inherited in a Mendelian fashion, which of the following is true? a) All the brown mice must have the same genotype for the fur color gene b) All the white mice must have the same genotype for the fur color gene c) If a brown F1 mouse were crossed to a white mouse, the offspring would all be brown d) A cross between two white F2 mice will produce both brown and white mice

b) All the white mice must have the same genotype for the fur color gene

What is the benefit of the repressor being constitutively produced in the lac operon? a) The repressor provides a feedback loop preventing the lac operon from being transcribed in the absence of glucose. b) The bacteria does not want to expend energy creating lactose metabolizing enzymes if lactose is not available. c) The repressor acts as a lactose sensor, and recruits RNA polymerase only in the presence of lactose. d) The operator needs either a constitutively

b) The bacteria does not want to expend energy creating lactose metabolizing enzymes if lactose is not available.

When you cross a plant from the purple-flowered line with a plant from the pink-flowered line, the offspring plants always have purple flowers. You have performed this cross many times, with different plants as the male and female parents, and always see the same result. If flower color is controlled by a single gene, which allele is dominant, and which is recessive? a) The pink allele is dominant, while the purple allele is recessive b) The purple allele is dominant, while the pink allele is recessive c) The purple and pink alleles are both dominant d) The purple and pink alleles are both recessive

b) The purple allele is dominant, while the pink allele is recessive

What essential difference between prokaryotes and multicellular eukaryotes most likely explains why eukaryotes have far more sophisticated regulatory mechanisms? a) Prokaryotes do not have a nucleus, while eukaryotes do. b) While prokaryotes grow and divide, multicellular eukaryotes develop and differentiate into different complex tissues. c) Eukaryotic DNA, unlike prokaryotic DNA, is tightly packaged into chromatin. d) Eukaryotes and prokaryotes employ all of the same regulatory mechanisms, there is no difference between them.

b) While prokaryotes grow and divide, multicellular eukaryotes develop and differentiate into different complex tissues.

11. Before transcription of the lac operon can occur, RNA polymerase must bind strongly to the promoter. This happens when a) CAP binds to the CAP site in the promoter. b) a CAP-cAMP complex binds to the CAP site in the promoter. c) catabolite repression occurs. d) lacI+ is mutated to lacI-.

b) a CAP-cAMP complex binds to the CAP site in the promoter.

13. Trans-dominant genes a) affect upstream or downstream genes on the same chromosome b) affect expression of genes located on another chromosome c) always lead to repression of genes on the same chromosome. d) always lead to expression of genes on a different chromosome.

b) affect expression of genes located on another chromosome

The order of the structural genes in the lac operon is a.3'-lacY-lacA-lacZ-5'. b. 5'-lacZ-lacY-lacA-3'. c. 3'-lacZ-lacY-lacA-5'. d. 5'-lacA-lacY-lacZ-3'. e. 5'-lacY-lacZ-lacA-3'.

b. 5'-lacZ-lacY-lacA-3'.

Which of the following mutations could lead to constitutive expression of the genes of the lac operon? a. A mutation in the lac-Z gene b. A mutation in the operator sequence c. A super repressor mutation d. A mutation in the lac-Y gene

b. A mutation in the operator sequence

HREs are a. proteins that interact with histones. hormone receptors. b. DNA sequences in promoter regions to which steroid hormone receptors bind. c. elements that lead to histone deacetylation. d. None of these

b. DNA sequences in promoter regions to which steroid hormone receptors bind.

What is the role of glucose in catabolite repression? a. It increases the levels of cAMP in the cell, stimulating transcription from the lac operon. b. It decreases the levels of cAMP in the cell, repressing transcription from the lac operon. c. It stimulates transcription from the lac operon, causing an increase in cAMP levels in the cell. d. It represses transcription from the lac operon, causing a decrease in cAMP levels in the cell.

b. It decreases the levels of cAMP in the cell, repressing transcription from the lac operon

Which of the following best describes the biological role of the lac operon? a. It ensures that bacterial cells produce lactose only when no other food sources are available. b. It ensures that a cell dedicates resources to the production of enzymes involved in lactose metabolism only when lactose is available in the environment. c. It ensures that a cell produces enzymes involved in lactose metabolism in a constitutive manner. d. It prevents other sugars from being metabolized until all available lactose has been used.

b. It ensures that a cell dedicates resources to the production of enzymes involved in lactose metabolism only when lactose is available in the environment.

What would be the effect of a mutation in the lacI gene that prevented the repressor from binding to lactose? a. The lac Z, Y, and A genes would be induced by lactose. b. The lac Z, Y, and A genes would not be expressed. c. The lac Z, Y, and A genes would be expressed constitutively. d. The lac Z, Y, and A genes would be repressed by lactose.

b. The lac Z, Y, and A genes would not be expressed.

In eukaryotic cells, steroid hormones a. cause maternal effect. b. bind to cytoplasmic receptors, are transported to the nucleus, bind DNA, and regulate gene expression. c. bind to cell surface receptors and send signals that result in regulation of genes in the nucleus. d. act as enhancers and bind to an assortment of activators and repressors. e. methylate DNA to regulate gene expression.

b. bind to cytoplasmic receptors, are transported to the nucleus, bind DNA, and regulate gene expression.

In his experiments, Mendel noted that when two traits are involved in a genetic cross, they are inherited independently of each other. The reason for this is that a. genes on the same chromosome separate during the formation of gametes. b. genes on different chromosomes separate during the formation of gametes. c. chromosomes often recombine. d. alleles on the same chromosome separate during the formation of gametes. e. alleles on the same gene separate during the formation of gametes.

b. genes on different chromosomes separate during the formation of gametes.

Suppose you cross a pure-breeding (homozygous) black-coated male dog with curly fur to a pure-breeding, yellow-coated female dog with straight fur. In the next F1 generation, all the dogs, both male and female, have straight, black coats. You interbreed these F1 dogs with one another to get an additional F2 generation. If coat color and coat texture are controlled by two autosomal genes that assort independently, what fraction of F2 puppies will have yellow, straight fur? a) 3/4 b) 1/4 c) 3/16 d) 1/16

c) 3/16

The effect of allolactose is: a) Dissociation of RNA polymerase from DNA, terminating transcription of genes regulated by the lac operon b) Enhancement of binding of RNA polymerase to DNA, increasing gene transcription c) Conformational change in the repressor protein, inducing the lac operon d) Repression of the lac operon when glucose is present

c) Conformational change in the repressor protein, inducing the lac operon

Which statement best describes the relationship between genotype and phenotype? a) Genotype always completely determines phenotype b) Phenotype always completely determines genotype c) Genotype determines phenotype, but with influence from the environment d) Phenotype determines genotype, but with influence from the environment

c) Genotype determines phenotype, but with influence from the environment

Transcriptionally active regions of DNA, such as some promoters, are a) complexed with histone proteins. b) heavily methylated. c) sensitive to digestion with DNase I. d) resistant to digestion with DNase I.

c) sensitive to digestion with DNase I.

In a lacI- cell, expression of the lac operon is still low in the presence of glucose because of catabolite repression. lactose repression. attenuation. lactose induction.

catabolite repression.

Change in the DNA-histone complex that can increase or decrease transcriptional activity is termed induction. chromatin remodeling. nucleosome formation. gene regulation. None of these

chromatin remodeling

A lacOC mutation is constitutive. codominant incompletely dominant. recessive. cis-dominant.

constitutive

. Modifications to histone tails such as deacetylation by ______________, allow repressed genes to become transcriptionally active. This occurs in ___________ heterochromatin. a) Lysine acetyl transferases (KATs); constitutive b) Lysine acetyl transferases (KATs); facultative c) Histone deacetylases (HDACs); constitutive d) Histone deacetylases (HDACs); facultative

d) Histone deacetylases (HDACs); facultative

In a bacteria possessing the lac operon, which of the following occurs when glucose is low and lactose is abundant? a) Beta-galactosidase acetylases the operon b) Lactose permease cleaves lactose to glucose and galactose c) Lactose metabolism is increased by lactose binding to the operon d) Transport of lactose into the cell is enhanced

d) Transport of lactose into the cell is enhanced

Which statements about the modification of chromatin structure in eukaryotes is false? a. Some forms of chromatin modification can be passed on to future generations of cells. b. Methylation of histone tails in chromatin can promote condensation of the chromatin. c. Acetylation of histone tails is a reversible process. d. Deacetylation of histone tails in chromatin loosens the association between nucleosomes and DNA. e. DNA is not transcribed when chromatin is packaged tightly in a condensed form. f. Acetylation of histone tails in chromatin allows access to DNA for transcription.

d. Deacetylation of histone tails in chromatin loosens the association between nucleosomes and DNA.

Which of the following would be true of a plant heterozygous for a single gene controlling flower color? (Assume complete dominance). a. It displays the recessive flower color. b. About half of all its progeny will display the recessive flower color. c. It will produce gametes with recessive flower color alleles and gametes with dominant flower color alleles in about a 3:1 ratio. d. If crossed with another heterozygous plant, the majority of progeny will have the dominant flower color.

d. If crossed with another heterozygous plant, the majority of progeny will have the dominant flower color.

Which of the following plays a role in chromatin remodeling? a. histone acetyl transferases b. histone deacetylases c. SWI/SNF d. all of the above

d. all of the above

Removal of the 5' G-cap of mRNA transcripts a. extends mRNA half-life. b. reduces mRNA half-life. c. leads to polyadelylation. d. leads to degradation by exonucleases. e. prevents transcript transport.

d. leads to degradation by exonucleases.

In humans, brown eye color (B) is dominant to blue eyes (b). A brown-eyed man marries a woman with brown eyes and they have three blue-eyed daughters. What are the genotypes of the man and the woman? a. BB and BB b. BB and Bb c. bb and bb d. Bb and bb e. Bb and Bb

e. Bb and Bb

A similarity between regulation of the lac operon in bacteria and the regulation of galactose utilization in yeast is that both pathways a. transcribe all the genes necessary as one polycistronic mRNA. b. use feedback inhibition to stop making their sugars. c. use a modified version of their sugars as inducers. d. are subject to catabolite repression. e. C and D only

e. C and D only

Operons can best be defined as a. operational mutations affecting gene expression. b. dominant alleles responsible for enzyme synthesis. c. a common mode of gene expression in bacteria. d. a balance between repressor and inducer molecules. e. a set of genes under common regulatory control.

e. a set of genes under common regulatory control.

Gene silencing is a form of regulation controlled by repressor proteins. True False

false

Noncoding RNAs called miRNAs are present in most eukaryote genomes and are involved in negatively regulating gene expression through degradation of mRNAs with complementary sequences. True False

false

longer poly(A) tails on mRNAs are associated with less translational activity. True False

false

Heterochromatin is associated with mRNA translation. heterozygotes. differential gene expression. gene silencing. A, B, and C only

gene silencing

Posttranscriptional control of gene expression does NOT occur at which of the following levels? alternative polyadenylation alternative splicing ribosome selection gene silencing

gene silencing

The __________ are arranged sequentially after the promoter.

genes of an operon

In peas, tall plants are dominant to short plants. A cross between a tall pea plant and a short pea plant results in half the progeny being tall, and the other half being short. Therefore, the tall parent plant is genotypically homozygous. heterozygous. hemizygous. homogeneous. monozygous.

heterozygous.

An individual with the dominant phenotype but an unknown genotype is testcrossed, and all of many generated offspring exhibit the dominant phenotype. The genotype of the unknown individual is homozygous dominant. heterozygous dominant. homozygous recessive. heterozygous recessive.

homozygous dominant.

For a given gene, HREs (steroid hormone response elements) are located in the promoter sequence. immediately after the start site of transcription. in an enhancer element. in the termination sequence.

in the promoter sequence

A(n) _________ is a specific small molecule that binds to a bacterial regulatory protein and changes its shape so that it cannot bind to an operator, thus switching an operon on.

inducer

In terms of regulation of gene expression, tryptophan and allolactose are examples of ________ molecules. effector terminator operator repressor inducer

inducer

In the lac operon in E. coli, a nonsense mutation in the ________ gene will result in a loss of β-galactosidase activity in the cell. lacY lacI lacZ Both A and B All of these

lacZ

Regulatory proteins bind to the _________ to control expression of the operon.

operator

1. A(n) _________ is a stretch of DNA consisting of an operator, a promoter, and genes for a related set of proteins, usually making up an entire metabolic pathway.

operon

A ______________ a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.

promoter

Proteins that are encoded by the same gene but differ in structure and function are the product of alternative splicing in pre-mRNA processing. Such protein variants are termed isoteins. isozymes. heteromeric proteins. allelomorphs. protein isoforms.

protein isoforms

A(n) ___________ codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes.

regulatory gene

A(n) _________ is a protein that inhibits gene transcription. In prokaryotes, this protein binds to the DNA in or near the promoter.

repressor

To inhibit the transcription of operon genes, the lacI gene product binds to beta galactosidase. the promoter. the operator. the repressor. the inducer.

the operator

Net or overall probabilities are obtained by multiplying separate independent probabilities. This is formally known as the sum rule. the product rule. the chi-square test. the sign test. the probability rule.

the product rule

DNase I-hypersensitive regions are usually located upstream from the start site of transcription. in the middle of a gene near intron splice sites. downstream from the promoter. in telomeric or centromeric regions.

upstream from the start site of transcription