exam 3

Question 1

Suppose nondisjunction involving a single chromosome occurs in meiosis I during gametogenesis for a mother egg cell. What fraction of her gametes will give rise to offspring with trisomy if they are fertilized by normal sperm?

Answer 1

1/2

Question 2

What is the mechanism of dosage compensation (different numbers of X chromosomes in males and females) in mammals?

Answer 2

transcription from genes on one X chromosome in females is suppressed, to match expression levels in males

Question 3

Thymine dimers are most commonly caused by exposure to ______ .

Answer 3

UV radiation

Question 4

Which of these point mutations is most likely to produce a null allele (no function in a gene)?

A single nucleotide insertion in the first exon of a gene

Three-nucleotide insertion in the first exon of a gene

A missense mutation

A mutation in the 5’ upstream region

A transversion mutation

Answer 4

A single nucleotide insertion in the first exon of a gene

Question 5

During the phenomenon of RNA interference, what do miRNAs target for destruction?

Answer 5

mRNA complementary to the miRNA

Question 6

refers to a site or mutation that only affects expression of genes on the same piece of DNA

Answer 6

cis-dominant

Question 7

a site at which a transcription factor binds to activate gene expression of a target gene

Answer 7

enhancer

Question 8

a site at which a transcription factor binds to repress gene expression of a target gene

Answer 8

operator

Question 9

a series of genes expressed as one common transcript

Answer 9

operon

Question 10

a small molecule that binds to a protein and changes its function, allowing gene expression to occur

Answer 10

inducer

Question 11

In the presence of glucose and absence of lactose, where is the lac repressor bound?

Answer 11

lacO

Question 12

Which of the following statements is true about the GAL genes in yeast?

In the presence of galactose, galactose binds to Gal4 to cause conformational changes in the protein, leading to GAL gene expression.

In the presence of galactose, Gal80 does not inhibit Gal4 and therefore Gal4 activates GAL gene expression.

In the presence of galactose, Gal80 binds to Gal4 to activate GAL gene expression.

In the presence of galactose, Gal4 binds to an upstream silencer sequence to inhibit GAL gene expression.

In the presence of galactose, Gal80 binds to an upstream activator sequence to activate GAL gene expression.

Answer 12

In the presence of galactose, Gal80 does not inhibit Gal4 and therefore Gal4 activates GAL gene expression.

Question 13

Which of the following domains would you expect to find in the transcription factor that activates gene expression when cells are exposed to the steroid hormone estrogen?

estrogen binding domain

DNA binding domain

transcription activation domain

two of the above

all of the above

Answer 13

all of the above

Question 14

Transposable elements are DNA sequences that can

Answer 14

move to new location within the genome of one cell

Question 15

You have conducted an Ames test on a given compound. Which of the following would be classified as a positive result on the Ames test?

Answer 15

when a his- strain now grows on a plate without histidine

Question 16

The fluctuation test allowed Luria and Delbruck to conclude that ________.

Answer 16

Mutations occur in the absence of environmental challenges

Question 17

Which of the following protein complexes links transcription activator proteins to the preinitiation complex?

Answer 17

Mediator

Question 18

A mutant E. coli strain, grown in the presence of lactose and absence of glucose, does not produce beta-galactosidase protein. Which of the following mutations could not lead to this phenotype?

Answer 18

lacOc

Question 19

What do regulation of the bacterial lac operon and yeast GAL genes have in common?

Answer 19

these two are true for both:

a) a small molecule inside the cell binds to a protein and causes it to changes in its conformation (Lac Rep and GAL3)

b) the presence of a small molecule in the environment leads to expression of the operon (lactose, galactose)

Question 20

Which statement is true about DNA methylation in bacteria?

it is used to regulate mutation repair

it is used to regulate accessibility of transcription factor binding sites in chromatin

it is used to regulate DNA replication

it is used to regulate transcription termination

it is used to regulate protein translation

Answer 20

it is used to regulate mutation repair

Question 21

Which of the following statements is/are true about epigenetics?

1. Epigenetic changes involve changes in DNA methylation and histone modification.
2. Epigenetic changes do not involve alterations in the DNA sequence.
3. Epigenetic changes affect DNA accessibility and chromatin structure.
4. Epigenetic changes affect patterns of gene expression.
5. Epigenetic effects are reversible.
6. Epigenetic effects can last from early developmental stage to late developmental stage.

Answer 21

all of the above

Question 22

What effect does methylation of CpG islands have on human promoters?

Answer 22

reduced transcription

Question 23

Loss-of-function mutations in which two of the following lead to a Lac minus phenotype in E. coli?

Answer 23

lacZ and lacY

Question 24

Interacalating agents generally result in which type of mutagenic event?

Answer 24

frameshift mutation

Question 25

Which of these is an allosteric regulator of a prokaryotic transcription factor?

Answer 25

allolactose

Question 26

E. coli is growing in a solution containing glucose and lactose. After it consumes the last of the glucose, the levels of cyclic AMP in the cell begin to rise. What effect would this have on protein binding at the lac operon?

Answer 26

it would cause more CAP to be bound, and more polymerase to be bound

Question 27

Which of these haploid strains does not produce permease and does not produce β-galactosidase? 1. I- P+ O+ Z+ Y+ 2. I+ P+ O+ Z- Y+ 3. I- P+ O+ Z- Y- 4. I+ P+ Oc Z+ Y+ 5. I- P+ O+ Z+ Y-

Answer 27

3

Question 28

Which statement is true about DNA methylation in eukaryotes?

Answer 28

it is used to regulate the chromatin state (open or closed) at a gene

Question 29

In humans, how many chromosomes would be found in the nuclei of somatic cells that were triploid?

Answer 29

69

Question 30

In humans, how many chromosomes would be found in the nuclei of somatic cells that were monosomic ?

Answer 30

45

Question 31

In humans, how many chromosomes would be found in the nuclei of somatic cells that were trisomic ?

Answer 31

47

Question 32

In humans, how many chromosomes would be found in the nuclei of somatic cells that were diploid ?

Answer 32

46

Question 33

If a transposon integrates into the promoter of a gene, what is the most likely outcome for the protein made by that gene?

Answer 33

decreased amount of the normal protein

Question 34

Which of the following is most likely characteristic of open promoters?

Answer 34

They are in a euchromatic region.

Question 35

a mutation that causes a change from purine to pyrimidine or from pyrimidine to purine

Answer 35

transversion mutation

Question 36

Which of the following conditions will result in the greatest level of transcription of the lac operon?

Answer 36

lactose and cAMP present, glucose absent

Question 37

Which of the following statements about enhancers is UNLIKELY to be true? Enhancers can be in the intron of a gene. There can be more than one enhancer for a gene. Enhancers can be in the same orientation or opposite orientation to the gene to be regulated. Enhancers can be nearby or at great distance from the gene it controls. Enhancers are always at or near the promoter.

Answer 37

Enhancers are always at or near the promoter.

Question 38

If a 21 bp deletion occurred in the gene for the human glucocorticoid receptor (a steroid hormone receptor) and that deletion caused a mutant version of the protein to be made in which the function of the DNA-binding domain was destroyed, but the functions of other domains in the protein were still fine, where would you expect to find this protein in the absence and presence of hormone?

Answer 38

In the absence of hormone the protein would be found in the cytoplasm; in the presence of hormone the protein would be found in the nucleus -without the hormone binding domain, the protein would never bind hormone, never change shape, never release HSP90, and stay in the cytoplasm al the time -without the DNA-binding domain the protein would be in the cytoplasm as usual in the absence of hormone; in the presence of hormone it would move into the nucleus as usual, but be unable to bind DNA -without the transcription activation domain the protein would be in the cytoplasm as usual in the absence of hormone; in the presence of hormone it would move into the nucleus as usual, bind DNA, but be unable to activate transcription of the gene