Question 1

Forms of the Ras protein found in tumors usually cause which of the following events to occur?
A) DNA replication to stop
B) decreased cell-to-cell adhesion
C) cell division to cease
D) excessive cell division

Accepted Answer

Forms of the Ras protein found in tumors typically lead to excessive cell division. This is because mutations in the Ras protein often result in its constitutive activation, promoting continuous cell proliferation and contributing to cancer development.

Question 2

If a mutation alters a maternal effect gene in a female Drosophila zygote, which of the following is most likely to occur?
A) She will not develop past the early embryonic stage.
B) All of her offspring will show the mutant phenotype, regardless of their genotype.
C) Only her male offspring will show the mutant phenotype.
D) Only her female offspring will show the mutant phenotype.

Accepted Answer

Maternal effect genes are those whose mRNA or protein products are deposited in the egg by the mother and are crucial for early development. If a mutation occurs in one of these genes in a female Drosophila, it affects the development of her offspring because they rely on the maternal gene products present in the egg for their early development stages. Therefore, all of her offspring will exhibit the mutant phenotype, regardless of their own genotype, because the phenotype is determined by the maternal genotype for these specific genes.

Question 3

The product of the bicoid gene in Drosophila is responsible for determining which of the following embryonic features or structures during development?
A) orientation of the dorsal-ventral axis
B) orientation of the left-right axis
C) segmentation of developing limbs
D) orientation of the anterior-posterior axis

Accepted Answer

The product of the bicoid gene in Drosophila is a protein that functions as a transcription factor, crucial for establishing the anterior-posterior axis in the early embryo. It forms a concentration gradient with higher levels at the future anterior end, guiding the development of head and thorax structures.

Question 4

Which of the following statements correctly describes a characteristic of tumor-suppressor genes?
A) They are frequently overexpressed in cancerous cells.
B) They are cancer-causing genes introduced into cells by viruses.
C) They encode proteins that help prevent uncontrolled cell growth.
D) They often encode proteins that stimulate the cell cycle.

Accepted Answer

Tumor-suppressor genes encode proteins that help prevent uncontrolled cell growth, acting as a brake on cell division and playing a crucial role in protecting against cancer.

Question 5

Muscle cells differ from nerve cells mainly because they ________.
A) express different genes
B) contain different genes
C) use different genetic codes
D) have unique ribosomes

Accepted Answer

Muscle cells and nerve cells contain the same set of genes but differ in which genes are expressed. Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product, such as a protein, which leads to the differentiation of cells into various types like muscle and nerve cells.

Question 6

Which of the following explains why introducing the MyoD protein into a fat cell causes that cell to become a muscle cell but adding it to a neuron will have no effect?
A) Fat cells are undifferentiated, the MyoD protein causes them to differentiate.
B) Neurons are a differentiation step after muscle cells, they cannot go "backwards."
C) Muscle-specific gene expression requires a protein that neurons do not make.
D) MyoD is causes positive feedback of MyoD expression in fats cells but not neurons.

Accepted Answer

Muscle-specific gene expression, which is initiated by MyoD, requires additional proteins that are present in fat cells but not in neurons. This is why MyoD can convert fat cells into muscle cells but has no effect on neurons, as the latter lack the necessary cofactors for muscle gene activation.

Question 7

Which of the following describes the role typical proto-oncogenes have when they are expressed in cells that are not cancerous?
A) They suppress tumor growth.
B) They inhibit differentiation.
C) They stimulate normal cell growth and division.
D) They enhance signaling from growth factor receptors.

Accepted Answer

Proto-oncogenes play a crucial role in promoting normal cell growth and division. When these genes are mutated, they can become oncogenes that contribute to cancer development by allowing uncontrolled cell proliferation.

Question 8

If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then ________.
A) the amino acid inactivates the repressor
B) the repressor is active in the absence of the amino acid
C) the amino acid acts as a corepressor
D) the amino acid turns on transcription of the operon

Accepted Answer

The trp operon is a repressible operon where the presence of the amino acid (tryptophan) acts as a corepressor, activating the repressor to bind to the operator and inhibit transcription.

Question 9

Which of the following conclusions is consistent with the fact that plants can be cloned from somatic cells?
A) Differentiated cells retain all the genes of the zygote.
B) Differentiation results in the loss of non-expressed genes.
C) The differentiated state is normally very unstable.
D) Differentiation does not occur in plants.

Accepted Answer

Differentiated cells retaining all the genes of the zygote is a prerequisite for the possibility of cloning plants from somatic cells. This implies that despite differentiation, the cells maintain the full genetic blueprint necessary for the development of a new organism.

Question 10

Cell differentiation always involves ________.
A) transcription of the myoD gene
B) the movement of cells
C) the production of tissue-specific proteins
D) the selective loss of certain genes from the genome

Accepted Answer

Cell differentiation involves the production of tissue-specific proteins, which are crucial for the specialized functions of different cell types. This process is guided by the selective expression of genes rather than the loss of genes from the genome or the transcription of a specific gene like myoD in all cell types.

Question 11

Cytoplasmic determinants are best described as having which of the following characteristics?
A) They are maternal substances in the egg that influence the course of early development.
B) They are single-stranded RNA molecules capable of binding complementary sequences and altering translation.
C) They are centromeric regions of DNA loosened for chromosomal replication by transcription factors.
D) They are tissue-specific transcription factors expressed in the early embryo.

Accepted Answer

Cytoplasmic determinants are maternal substances present in the egg before fertilization, which play a crucial role in early development by influencing the developmental fate of cells.

Question 12

Which of the following characterizes BRCA1 and BRCA2 as tumor-suppressor genes?
A) Their normal products participate in repair of DNA damage.
B) The mutant forms of either one of these prevent breast cancer.
C) The normal genes code for estrogen receptors.
D) They block penetration of breast cells by chemical carcinogens.

Accepted Answer

BRCA1 and BRCA2 are involved in the repair of DNA damage, which is a crucial function in preventing the development of cancer. When DNA repair mechanisms are compromised due to mutations in these genes, cells are more likely to accumulate additional mutations that can lead to cancer.

Question 13

In wildtype Drosophila embryos, the bicoid mRNA is localized to the anterior end of the embryo. If bicoid mRNA was injected into the embryo's posterior end as well, which of the following developmental events would occur?
A) The embryo would grow extra wings and legs.
B) The embryo would have altered segmentation.
C) The embryo would show anterior structures at both ends of the embryo.
D) The embryo would develop normally.

Accepted Answer

Bicoid mRNA is a morphogen that specifies anterior structures in Drosophila embryos. Injecting it into the posterior end would result in the formation of anterior structures (such as the head and thorax) at both ends of the embryo.

Question 14

Which of the following types of mutation would convert a proto-oncogene into an oncogene?
A) a mutation that blocks transcription of the proto-oncogene
B) a mutation that greatly reduces the stability of a proto-oncogene mRNA
C) a mutation that greatly increases the amount of the proto-oncogene protein
D) a deletion of most of the proto-oncogene coding sequence

Accepted Answer

A mutation that greatly increases the amount of the proto-oncogene protein can convert a proto-oncogene into an oncogene by leading to overactive cell growth signaling, potentially causing cancer.

Question 15

The functioning of enhancers is an example of ________.
A) a eukaryotic equivalent of prokaryotic promoter functioning
B) transcriptional control of gene expression
C) the stimulation of translation by initiation factors
D) post-translational control that activates certain proteins

Accepted Answer

Enhancers are DNA sequences that increase the rate of transcription of genes, representing a mechanism of transcriptional control of gene expression in eukaryotes. They do not directly participate in translation or post-translational processes, nor are they equivalent to prokaryotic promoters in function.

Question 16

In colorectal cancer, several genes must be mutated for a cell to develop into a cancer cell. Which of the following kinds of genes would you expect to be mutated?
A) genes coding enzymes that act in the colon
B) genes involved in control of the cell cycle
C) genes that are especially susceptible to mutation
D) genes regulating cell division in colon bacteria

Accepted Answer

Genes involved in the control of the cell cycle are critical for maintaining normal cell growth and division. Mutations in these genes can lead to uncontrolled cell proliferation, a hallmark of cancer.

Question 17

Mutations in which of the following genes result in transformations in the identity of entire body parts?
A) segmentation genes
B) egg-polarity genes
C) homeotic genes
D) inducers

Accepted Answer

Homeotic genes are responsible for determining the identity of body parts during development. Mutations in these genes can lead to transformations where one body part develops the characteristics of another, such as legs where antennae should be.

Question 18

A cell is considered to be differentiated if it has which of the following characteristics?
A) The cell replicates by the process of mitosis.
B) The cell loses connections to the surrounding cells.
C) The cell produces proteins specific to a particular cell type.
D) The cell appears to be different from the surrounding cells.

Accepted Answer

Differentiation refers to the process by which a cell becomes specialized to perform a specific function. This specialization often involves the production of proteins that are unique to that cell type, enabling it to carry out its specific role in the organism.

Question 19

Which of the following describes the normal function of the p53 gene product?
A) It inhibits the cell cycle.
B) It slows down the rate of DNA replication by interfering with the binding of DNA polymerase.
C) It causes cells to reduce expression of genes involved in DNA repair.
D) It allows cells to pass on mutations due to DNA damage.

Accepted Answer

The p53 gene product functions as a tumor suppressor by inhibiting the cell cycle. This allows time for DNA repair mechanisms to correct any damage before the cell proceeds to divide, thereby preventing the propagation of mutations.

Question 20

A genetic test to detect predisposition to cancer would likely examine the APC gene for involvement in which type(s) of cancer?
A) colorectal only
B) lung and breast
C) lung only
D) lung and prostate

Accepted Answer

The APC gene is most notably associated with colorectal cancer, particularly in familial adenomatous polyposis (FAP), which can lead to a high risk of developing colorectal cancer if not managed.

Quiz 18: Control of Gene Expression

Forms of the Ras protein found in tumors usually cause which of the following events to occur?

If a mutation alters a maternal effect gene in a female Drosophila zygote, which of the following is most likely to occur?

The product of the bicoid gene in Drosophila is responsible for determining which of the following embryonic features or structures during development?

Which of the following statements correctly describes a characteristic of tumor-suppressor genes?

Muscle cells differ from nerve cells mainly because they ________.

Which of the following explains why introducing the MyoD protein into a fat cell causes that cell to become a muscle cell but adding it to a neuron will have no effect?

Which of the following describes the role typical proto-oncogenes have when they are expressed in cells that are not cancerous?

If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then ________.

Which of the following conclusions is consistent with the fact that plants can be cloned from somatic cells?

Cell differentiation always involves ________.

Cytoplasmic determinants are best described as having which of the following characteristics?

Which of the following characterizes BRCA1 and BRCA2 as tumor-suppressor genes?

In wildtype Drosophila embryos, the bicoid mRNA is localized to the anterior end of the embryo. If bicoid mRNA was injected into the embryo's posterior end as well, which of the following developmental events would occur?

Which of the following types of mutation would convert a proto-oncogene into an oncogene?

The functioning of enhancers is an example of ________.

In colorectal cancer, several genes must be mutated for a cell to develop into a cancer cell. Which of the following kinds of genes would you expect to be mutated?

Mutations in which of the following genes result in transformations in the identity of entire body parts?

A cell is considered to be differentiated if it has which of the following characteristics?

Which of the following describes the normal function of the p53 gene product?

A genetic test to detect predisposition to cancer would likely examine the APC gene for involvement in which type(s) of cancer?