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Questions and Answers of Biology

Describe the two assumptions that underlie the identification of disease-causing alleles via haplotypes.
What is the purpose of the International HapMap Project? How will it help researchers who study disease-causing alleles?
What is a prion? Explain how a prion relies on normal cellular proteins to cause a disease such as mad cow disease.
Some people have a genetic predisposition for developing prion diseases. Examples are described in Table 24.6. In the case of Gerstmann-Straussler-Scheinker disease, the age of onset is typically at
Explain, at the molecular level, why human genetic diseases often follow a simple Mendelian pattern of inheritance, whereas most normal traits, such as the shape of your nose or the size of your
What four types of cellular processes must occur to enable a fertilized egg to develop into an adult multicellular animal? Briefly discuss the role of each process.
Discuss how the anterior portion of the anteroposterior axis is established. What aspects of oogenesis are critical in establishing this axis? What do you think would happen if the bicoid mRNA was
Describe the function of the Bicoid protein. Explain how its ability to exert its effects in a concentration-dependent manner is a critical feature of its function.
With regard to development, what are the roles of the maternal-effect genes versus the zygotic genes? Which types of genes are needed earlier in the development process?
Discuss the role of homeotic genes in development. Explain what happens to the phenotype of a fly when a gain-of-function homeotic gene mutation causes the protein to be expressed in an abnormal
Describe the molecular features of the homeobox and homeodo-main. Explain how these features are important in the function of homeotic genes.
If a mutation in a homeotic gene produced the following phenotypes, would you expect the mutation to be a loss-of-function or a gain-of-function allele? Explain your answer. A. An abdominal segment
Explain how loss-of-function mutations in the following categories of genes would affect the morphologies of Drosophila larvae: A. Gap genes B. Pair-rule genes C. Segment-polarity genes
What is the difference between a maternal-effect gene and a zygotic gene? Of the following genes that play a role in Drosophila development, which are maternal-effect genes and which are zygotic?
The arrangement of body axes of the fruit fly are shown in Figure 25.5g. Are the following statements true or false with regard to body axes in the mouse? A. Along the anteroposterior axis, the head
Cloning of mammals (such as Dolly) is described in Chapter 21. Based on your understanding of animal development, explain why an enucleated egg is needed to clone mammals. In other words, what
A hypothetical cell lineage is shown here.A gene, which we will call gene X, is activated in the B-l cell, so the B-l cell will progress through the proper developmental stages to produce three nerve
What is a heterochronic mutation? How does it affect the phenotypic outcome of an organism? What phenotypic effects would you expect if a heterochronic mutation affected the cell lineage that
Discuss the similarities and differences between the bithorax and Antennapedia complexes in Drosophila and the Hox gene complexes in mice.
What is cell differentiation? Discuss the role of myogenic bHLH proteins in the differentiation of muscle cells. Explain how they work at the molecular level. In your answer, indicate how protein
The MyoD gene in mammals plays a role in skeletal muscle-cell differentiation, whereas the Hox genes are homeotic genes that play a role in the differentiation of particular regions of the body.
What is a totipotent cell? In the following examples, which cells would be totipotent? A. Humans B. Corn C. Yeast D. Bacteria
What is a meristem? Explain the role of meristems in plant development.
Discuss the morphological differences between animal and plant development. How are they different at the cellular level? How are they similar at the genetic level?
Predict the phenotypic consequences of each of the following mutations: A. Apetalal defective B. Pistillata defective C. Apetalal and pistillata defective
If you observed fruit flies with the following developmental abnormalities, would you guess that a mutation has occurred in a segmentation gene or a homeotic gene? Explain your guess. A. Three
Explain how alternative splicing affects sex determination in Drosophila.
Which of the following statement(s) is/are true with regard to positional information in Drosophila? A. Morphogens are a type of molecule that conveys positional information. B. Morphogenetic
Discuss the morphological differences between the parasegments and segments of Drosophila. Discuss the evidence, providing specific examples, that suggests the parasegments of the embryo are the
Here are schematic diagrams of mutant larvae.The left side of each pair shows a wild-type larva, with gray boxes showing the sections that are missing in the mutant larva. Which type of gene is
Describe what a morphogen is and how it exerts its effects. What do you expect will happen when a morphogen is expressed in the wrong place in an embryo? List five examples of morphogens that
What is the meaning of positional information? Discuss three different ways that cells obtain positional information. Which of these three ways do you think is the most important for the formation of
Gradients of morphogens can be preestablished in the oocyte. Also, later in development, morphogens can be secreted from cells. How are these two processes similar and different?
Researchers have used the cloning methods described in Chapter 20 to clone the bicoid gene and express large amounts of the Bicoid protein. The Bicoid protein was then injected into the posterior end
Two techniques commonly used to study the expression patterns of genes that play a role in development are Northern blotting and in situ hybridization. As described in Chapter 20, Northern blotting
Explain one experimental strategy for determining the functional role of the mouse HoxD-3 gene.
In the experiment of Figure 25.16, suggest reasons why the n536, n355, and n540 strains have an egg-laying defect.
Another way to study the role of proteins (e.g., transcription factors) that function in development is to microinject the mRNA that encodes a protein, or the purified protein itself, into an oocyte
Why have geneticists used reverse genetics to study the genes involved in vertebrate development? Explain how this strategy differs from traditional genetic analyses like those done by Mendel.
Compare and contrast the experimental advantages of Drosophila and C. elegans in the study of developmental genetics.
What is meant by the term cell fate? What is a cell lineage diagram? Discuss the experimental advantage of having a cell lineage diagram. What is a cell lineage?
Explain why a cell lineage diagram is necessary to determine if a mutation is heterochronic.
Explain the rationale behind the use of the "bag of worms" phenotype as a way to identify heterochronic mutations.
Here are the results of cell lineage analyses of hypodermal cells in wild-type and mutant strains of C. elegans.Explain the nature of the mutations in the altered strains.
Take a look at solved problem S3 before answering this question. Drosophila embryos carrying a ts mutation were exposed to the permissive (25°C) or nonpermissive (30°C) temperature at
All of the homeotic genes in Drosophila have been cloned. As discussed in Chapter 20, cloned genes can be manipulated in vitro. They can be subjected to cutting and pasting, site-directed
You need to understand solved problem S4 before answering this question. If the artificial gene containing the stripe 2 enhancer and the (β-galactosidase gene was found within an embryo that also
Compare and contrast the experimental advantages and disadvantages of Drosophila, C. elegans, mammals, and Arabidopsis.
At the molecular level, how do you think a gain-of-function mutation in a developmental gene might cause it to be expressed in the wrong place or at the wrong time? Explain what type of DNA sequence
What is the difference between a constitutive gene and a regulated gene?
What is diauxic growth? Explain the roles of cAMP and the catabolite activator protein in this process.
Mutations may have an effect on the expression of the lac operon and the trp operon. Would the following mutations have a cis- or trans-effect on the expression of the protein-encoding genes in the
Would a mutation that inactivated the lac repressor and prevented it from binding to the lac operator site result in the constitutive expression of the lac operon under all conditions? Explain. What
What is meant by the term attenuation? Is it an example of gene regulation at the level of transcription or translation? Explain your answer.
As described in Figure 14.12, four regions within the trpL mRNA can form stem-loops. Lets suppose that mutations have been previously identified that prevent the ability of a particular region to
As described in Chapter 13, enzymes known as aminoacyl-tRNA synthetases are responsible for attaching amino acids to tRNAs. Let's suppose that tryptophanyl-tRNA synthetase was partially defective at
The 3-4 stem-loop and U-rich attenuator found in the trp operon (see Figure 14.12) is an example of p-independent termination. The function of p-independent terminators is described in Chapter 12.
Mutations in tRNA genes can create tRNAs that recognize stop codons. Because stop codons are sometimes called nonsense codons, the types of mutations that affect tRNAs are called nonsense
Translational control is usually aimed at preventing the initiation of translation. With regard to cellular efficiency, why do you think this is the case?
In general, why is it important to regulate genes? Discuss examples of situations in which it would be advantageous for a bacterial cell to regulate genes.
A species of bacteria can synthesize the amino acid histidine so it does not require histidine in its growth medium. A key enzyme, which we will call histidine synthetase, is necessary for histidine
Using three examples, describe how allosteric sites are important in the function of genetic regulatory proteins.
In what ways are the actions of the lac repressor and trp repressor similar and how are they different with regard to their binding to operator sites, their effects on transcription, and the
Transcriptional repressor proteins (e.g., lac repressor), antisense RNA, and feedback inhibition are three different mechanisms that turn off the expression of genes and gene products. Which of these
If a gene is repressible and under positive control, describe what kind of effector molecule and regulatory protein are involved. Explain how the binding of the effector molecule affects the
Transcriptional regulation often involves a regulatory protein that binds to a segment of DNA and a small effector molecule that binds to the regulatory protein. Do the following terms apply to a
An operon is repressible-a small effector molecule turns off transcription. Which combinations of small effector molecules and regulatory proteins could be involved? A. An inducer plus a repressor B.
Some mutations have a c/5-effect, whereas others have a trans-effect. Explain the molecular differences between cis- and transmutations. Which type of mutation (cis or trans) can be complemented in a
What is enzyme adaptation? From a genetic point of view, how does it occur?
In the lac operon, how would gene expression be affected if one of the following segments was missing? A. lac operon promoter B. Operator site C. lacA gene
Answer the following questions that pertain to the experiment of Figure 14.7. A. Why was P-ONPG used? Why was no yellow color observed in one of the four tubes? Can you propose alternative methods to
Chapter 20 describes a blotting method known as Northern blotting, which can be used to detect RNA transcribed from a particular gene or a particular operon. In this method, a specific RNA is
As described in experimental question E2 and also in Chapter 20, the technique of Northern blotting can be used to detect the transcription of RNA. Draw the results you would expect from a Northern
An absentminded researcher follows the protocol described in Figure 14.7 and (at the end of the experiment) does not observe any yellow color in any of the tubes. Yikes! Which of the following
Explain how the data shown in Figure 14.9 indicate that two operator sites are necessary for repression of the lac operon. What would the results have been if all three operator sites were required
A mutant strain has a defective lac operator site that results in the constitutive expression of the lac operon. Outline an experiment you would carry out to demonstrate that the operator site must
Discuss the advantages and disadvantages of genetic regulation at the different levels described in Figure 14.1.
As you look at Figure 14.10, discuss possible "molecular ways" that the cAMP-CAP complex and lac repressor may influence RNA polymerase function. In other words, try to explain how the bending and
Discuss the common points of control in eukaryotic gene regulation.
Explain how phosphorylation affects the function of the CREB protein.
A particular drug inhibits the protein kinase that is responsible for phosphorylating the CREB protein. How would this drug affect the following events? A. The ability of the CREB protein to bind to
The glucocorticoid receptor and the CREB protein are two examples of transcriptional activators. These proteins bind to response elements and activate transcription. The answers to this question are
Transcription factors such as the glucocorticoid receptor and the CREB protein form homodimers and activate transcription. Other transcription factors form heterodimers. For example, a transcription
An enhancer, located upstream from a gene, has the following sequence: 5'-GTAG-3' 3'_CATC-5' This enhancer is orientation-independent. Which of the following sequences also works as an enhancer? A.
The DNA-binding domain of each CREB protein subunit recognizes the sequence 5'-TGACGTCA-3'. As a matter of random chance, how often would you expect this sequence to occur in the human genome, which
Solved problem S3 shows the locations of domains in the glucocorticoid receptor relative to the amino- and carboxyl-terminal ends of the protein. Make a drawing that illustrates the binding of a
The gene that encodes the enzyme called tyrosine hydroxylase is known to be up regulated by the CREB protein. Tyrosine hydroxylase is expressed in nerve cells and is involved in the synthesis of
What is a histone variant?
Discuss the structure and function of regulatory elements. Where are they located relative to the core promoter?
Explain how the acetylation of core histones may loosen chromatin packing.
What is meant by the term histone code? With regard to gene regulation, what is the proposed role of the histone code?
What is a nucleosome-free region? Where are they typically found in a genome? How are nucleosome-free regions thought to be functionally important?
What is an insulator? Describe two different ways that insulators may exert their effects.
What is DNA methylation? When we say that DNA methylation is heritable, what do we mean? How is it passed from a mother to a daughter cell?
What is a CpG island? Where would you expect one to be located? How does the methylation of CpG islands affect gene expression?
What is meant by the term transcription factor modulation? List three general ways that this can occur.
What are the functions of transcriptional activator proteins and repressor proteins? Explain how they work at the molecular level.
Are the following statements true or false? A. An enhancer is a type of regulatory element. B. A core promoter is a type of regulatory element. C. Regulatory transcription factors bind to regulatory
Transcription factors usually contain one or more motifs that play key roles in their function. What is the function of the following motifs? A. Helix-turn-helix B. Zinc finger C. Leucine zipper
Describe the steps that occur for the glucocorticoid receptor to bind to a GRE.

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