genetics chapter 21

1. what would be the effect on X inactivation of adding siRNAs that eliminated the products of the Xist gene 2. what would be the effect of X inactivation of adding siRNAs that eliminated the products of the jpx gene? a. only the parental X chromosome would become inactivated b. one of the two x chromosomes would become inactivated c. one of the maternal x chromosomes would become inactivated d. both of the x chromosomes would become inactivated e. neither of the x chromosomes would become inactivated

1. neither of the X chromosomes would become inactivated 2. neither of the X chromosomes would becoem inactivated

One of the genes that determine fur color in cats is located on the X‑chromosome. At this locus, there is an allele for black fur and an allele for orange fur. Heterozygous female cats display a patchwork of orange‑ and black‑colored fur, and are referred to as calico cats. This phenotype is a result of X‑chromosome inactivation in female cats. Which statement is true about X‑chromosome inactivation? a. One X‑chromosome is inactivated during early embryonic development, but can be reactivated later. b. A specific X‑chromosome is inactivated in each cell so that all cells have the same active X‑chromosome. c. One X‑chromosome is inactivated immediately after fertilization when the zygote is formed. d. A random X‑chromosome is inactivated in each cell during early embryonic development and forms a Barr body. e. Both X‑chromosomes are inactivated in each cell once the necessary DNA is copied to an autosome.

A random X‑chromosome is inactivated in each cell during early embryonic development and forms a Barr body.

Modifications to chromatin can affect transcriptional activity by changing the accessibility of DNA to the transcription machinery. The given descriptions are examples of various processes that may or may not cause remodeling of chromatin. Match each description to the effect it has on transcriptional activity caused by chromatin remodeling. Activates, inactivates, activations AND inactivates, or no effect: - Histone acetyltransferases attach acetyl groups to the N-terminus of histones - Histone deacetylases remove acetyl groups from the N-terminus of histones - Histone methylation occurs at different amino acids. - RNA polymerase II binds the start site of transcription.

Activates: Histone acetyltransferases attach acetyl groups to the N-terminus of histones Inactivates: Histone deacetylases remove acetyl groups from the N-terminus of histones (also methylated CpG islands are often close to transcriptional start sites) Activates and inactivates: Histone methylation occurs at different amino acids. No effect: RNA polymerase II binds the start site of transcription.

The promoter of gene A has histones that are acetylated on lysine 27 of histone H3, and the promoter of gene B has histones that are methylated on lysine 4 of histone H3. Which gene is being actively transcribed? gene B, because histone acetylation is associated with gene silencing gene A, because histone acetylation is associated with gene expression gene A, because histone acetylation is associated with gene silencing gene B, because histone methylation is associated with gene expression Both genes are actively transcribed because both of those marks are associated with gene expression.

Both genes are actively transcribed because both of those marks are associated with gene expression.

Certain behavioral traits in humans are believed to be encoded by the X chromosome. Examples of such traits include verbal ability and seeking social interactions. For these traits, research has shown that there is less variability between identical male twins than between identical female twins. Which phenomenon best explains these results? a. Male twins both get the same mitochondria from their mother. b. Only one X chromosome is active in females. c. Males have a Y chromosome, which is much smaller than the X. d. Females have double the amount of X expression so there's more room for error.

Only one X chromosome is active in females.

In Arabidopsis thaliana, the Flowering Locus C (FLC) gene codes for a regulatory protein that suppresses flowering. FLC is expressed in seedlings to prevent premature flowering. In mature plants, FLC expression decreases with cooler temperatures, and flowering occurs once sufficiently cool temperatures are reached. If small‑interfering RNA (siRNA) that is complementary to FLC mRNA is introduced, how would RNA interference (RNAi) affect flowering? a. RNAi would induce methylation of chromatin and repress flowering. b. RNAi would degrade FLC mRNA and stimulate flowering. c. RNAi would bind irreversibly to FLC mRNA and stimulate flowering. d. RNAi would degrade FLC mRNA and repress flowering. e. RNAi is found in prokaryotes and would not affect Arabidopsis.

RNAi would degrade FLC mRNA and stimulate flowering.

Which of these statements concerning maintenance of histone modifications is CORRECT? In the process of DNA replication, nucleosomes are integrated, allowing the proteins to be unevenly sourced between new DNA molecules. One model supports epigenetic marks recruiting enzymes to recognize, bind, and modify histones, thereby presenting the target modification. Some models predict a combination of new and old histones being utilized to reestablish epigenetic marks after replication in maintaining histones. Different modifications are maintained by few mechanisms at their primary level of change.

Some models predict a combination of new and old histones being utilized to reestablish epigenetic marks after replication in maintaining histones. This is a model supported through experimentation in Drosophila embryos that could explain histone maintenance even when epigenetic marks are lost during replication.

A researcher is studying histones in mouse cells that have just been acetylated. Which of these statements is TRUE of these histones? a. Acetyl groups have been removed to the tails of these histones. b. The chromatin formed with these histones will likely appear open. c. Acetylation increases chromatin compaction. d. The charge of these histones will be unchanged.

The chromatin formed with these histones will likely appear open. Acetylation leads to more open chromatin by loosening interactions between histones and DNA as well as interactions between nearby nucleosomes.

How does DNA methylation affect the structure of DNA?

The methyl group changes the physical shape of the major groove in the DNA helix.

Which gene is the key player in X-chromosome inactivation? Jpx Xite Xist none of these Tsix

Xist

Monozygotic twins have identical DNA sequences, yet twins can differ in some physical or behavioral traits. What evidence suggests that epigenetic effects may cause these phenotypic differences in monozygotic twins? a. Younger twins increase DNA methylation, whereas older twins increase histone acetylation. b. Older twins increase DNA methylation, whereas younger twins increase histone acetylation. c. Older twins have more similar DNA methylation and histone acetylation patterns than younger twins. d. Younger twins have more similar DNA methylation and histone acetylation patterns than older twins.

Younger twins have more similar DNA methylation and histone acetylation patterns than older twins.

CpG islands

a group of CG sequences that may be clustered near a promoter region of a gene. The methylation of the cytosine bases usually inhibits transcription.

If a deacetylase inhibitor were injected into a mouse brain, which of the following would you expect to occur? a. A general increase in gene expression would occur. b. A general increase or decrease in gene expression, depending on the gene, would occur. c. Acetyl groups would be removed from histones. d. A general decrease in gene expression would occur. e. Methyl groups would be removed from the DNA.

a. A general increase in gene expression would occur.

A beekeeper notices that her bee population is declining rapidly. Upon further study, she notices that there are no queen bees present in her population. She suspects this is due to exposure to an environmental agent. Which of the following could be a possible mechanism for the environmental agent? a. The environmental agent is a methyltransferase enzyme that acts on genes that encode queen bee characteristics. b. The environmental agent mimics a Dnmt3 siRNA. c. The environmental agent causes royal jelly to be produced in abnormally high amounts. d. The environmental agent inhibits Dnmt3. e. The environmental agent is causing extensive chromosome rearrangements within the genome of the queen bees.

a. The environmental agent is a methyltransferase enzyme that acts on genes that encode queen bee characteristics.

Place the molecular processes in order that cause one X chromosome in each female cell to be active and the other X chromosome to become inactivated. active X chromosome and inactive x chromosome options: - Xite expression promotes Tsix expression - Xist expression is suppressed - Jpx expression promotes Xist expression - Xist coats the chromosome - Xite expression promotes Xist expression Jpx expression is suppressed

active X chromosome: - Xite expression promotes Tsix expression - Xist expression is suppressed Inactive X chromosome: - Jpx expression promotes Xist expression - Xist coats the chromosome

Which is not true of X-chromosome inactivation? a. The X-chromosome inactivation process begins at a site called the X-inactivation center. b. Male cells do not undergo X-chromosome inactivation. c. All of these statements are true. d. X-chromosome inactivation silences one of the X-e. chromosomes in female cells during early development. X-chromosome inactivation is not a reversable process.

all

What is the function of the gene Jpx? a. It encodes a long noncoding RNA that sustains the transcriptional activity of Tsix on the active X-chromosome. b. It encodes a long noncoding RNA that represses the transcriptional activity of Tsix on the inactive X-chromosome. c. It encodes a long noncoding RNA that stimulates the transcriptional activity of Xist on the inactive X-chromosome. d. It encodes a long noncoding RNA that stimulates the transcriptional activity of Xist on the active X-chromosome. e. It encodes a long noncoding RNA that represses the transcriptional activity of Xist on the active X-chromosome.

c. It encodes a long noncoding RNA that stimulates the transcriptional activity of Xist on the inactive X-chromosome.

Select the best example of transgenerational epigenetic inheritance. a. Vinclozolin binds to insulin receptors, disrupting glucose metabolism and causing epigenetic methylation of the insulin receptor gene. b. Experimental rats with nutrient‑restricted diets were at greater risk of infection than control rats that were fed a nutritionally‑complete diet. c. Offspring of rats with high‑fat diets were fed a low‑fat diet and had normal weights, but still developed symptoms of diabetes. d. A long non‑coding RNA transcribed from the Xist gene suppresses transcription of one X chromosome in each female mammal cell. e. Individuals with a history of childhood abuse have more methylation of the glucocorticoid receptor gene than individuals without such history.

c. Offspring of rats with high‑fat diets were fed a low‑fat diet and had normal weights, but still developed symptoms of diabetes.

What would be required to prove that a phenotype is caused by an epigenetic change? a. The phenotype must be the result of a nucleotide change that is present in one gender but not the other. b. The phenotype must be unexplained by known genetic mechanisms. c. The phenotype must be heritable with modified chromatin and an unaltered nucleotide sequence. d. The phenotype must be reversible in the presence of mutagenic compounds. e. The phenotype must be passed to progeny only through the maternal DNA.

c. The phenotype must be heritable with modified chromatin and an unaltered nucleotide sequence.

Which description is the best definition of a stem cell? a. a type of blood cell that does not have a nucleus, mitochondria, or other organelles b. a specialized cell that divides by meiosis to produce eggs or sperm in order to facilitate sexual reproduction c. an undifferentiated cell that can make countless copies of itself and differentiate into specialized cell types when appropriate d. a type of lymphocyte made in the thymus that contributes an adaptive immune response

c. an undifferentiated cell that can make countless copies of itself and differentiate into specialized cell types when appropriate

Mercury is a major pollutant in arctic ecosystems, and polar bears are particularly vulnerable to mercury contamination because it concentrates in the food they eat and then in their tissues. Some chemical pollutants are known to alter gene expression, but the mechanisms of these effects are unknown. A team of researchers was interested in whether mercury might affect gene expression in polar bears through epigenetic modifications. They examined levels of mercury and genome‑wide levels of DNA methylation in brain tissues from 4747 polar bears collected by local Inuit subsistence hunters. They measured DNA methylation with a technique called Luminometric Methylation Assay (LUMA), which uses methyl‑sensitive and methyl‑insensitive restriction endonucleases, followed by PCR and DNA sequencing, to measure genome‑wide DNA methylation. The results for male and female polar bears are shown. What conclusions can you draw from the data about epigenetic changes associated with mercury pollution in polar bears? a. Increased mercury levels in the brain correspond to increased DNA methylation in male polar bears. b. Increased mercury levels in the brain do not correspond to changes in DNA methylation in male or female polar bears. c. Increased mercury levels in the brain correspond to decreased DNA methylation in female polar bears. d. Increased mercury levels in the brain correspond to decreased DNA methylation in male polar bears. What predictions can you make about how gene expression in polar bears might be affected by mercury pollution? a. It is unlikely that mercury levels in the brain affect gene expression in male or female bears. b. Female bears with higher levels of mercury in the brain may exhibit higher levels of gene expression. c. Male bears with higher levels of mercury in the brain may exhibit lower levels of gene expression. d. Male bears with higher levels of mercury in the brain may exhibit higher levels of gene expression.

d. Increased mercury levels in the brain correspond to decreased DNA methylation in male polar bears. d. Male bears with higher levels of mercury in the brain may exhibit higher levels of gene expression.

What is the function of the gene Xite? a. It encodes a long noncoding RNA that represses the transcriptional activity of Tsix. b. It encodes a long noncoding RNA that represses the transcriptional activity of Xist. c. It encodes a long noncoding RNA that sustains the transcriptional activity of Xist. d. It encodes a long noncoding RNA that sustains the transcriptional activity of Tsix. e. It encodes a long noncoding RNA that represses the transcriptional activity of Jpx.

d. It encodes a long noncoding RNA that sustains the transcriptional activity of Tsix.

Which of these is NOT a type of histone modification? methylation acetylation ubiquitination dephosphorylation

dephosphorylation

What is the function of the gene Tsix? a. It produces long noncoding RNA that assists in the X-inactivation activity of Xist. b. It produces complementary antisense RNA that can bind to c. Xist and repress Xist transcription activity. c. It enhances the transcription activity of the gene Xite. d. It produces long noncoding RNA that recruits PRC2 to repress chromosome activity. e. It enhances the transcription activity of the gene Jpx.

e. It produces complementary antisense RNA that can bind to Xist and repress Xist transcription activity.

he inactivated X-chromosome can be visualized as a darkly stained structure in the nucleus of a female cell and is known as a(n)__________. a. X-inactivation center b. methylated chromosome c. nucleosome d. silent chromosome e. Barr body

e. barr body

When does X-chromosome inactivation occur in humans? a. immediately after conception b. during the second trimester of development c. in the first few weeks after birth d. right before birth e. in the first few weeks of development

e. in the first few weeks of development

There are several processes that lead to epigenetic changes on gene expression. Which of these mechanisms is matched correctly? DNA methylation: stimulates transcription histone acetylation: stimulates transcription histone methylation: stimulates transcription RNA molecules: repress transcription

histone acetylation: stimulates transcription

DNA methylation promotes what other chemical alteration of chromatin to suppress gene expression? histone deacetylation histone phosphorylation histone ubiquitylation DNA phosphorylation

histone deacetylation DNA methylation attracts histone deacetylase enzymes that remove acetyl groups from the tails of histone proteins. This alters chromatin structure in a way that represses transcription.

Heavily methylated DNA is usually associated with _____. a transcriptionally active gene repression of transcription open DNA between two nucleosomes DNA that is loosely wound around a histone

repression of transcription - Cytosine bases are often methylated to form 5-methylcytosine, which is associated with the repression of transcription.

Which gene encodes for a long noncoding RNA that coats the X-chromosome and attracts PRC2 to methylate H3K27 sites? Xist Tsix Xite Jpx none of these

xist