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Consider a hypothetical bacterial operon encoding genes needed for the degradation of compound X. Which statement is most likely to be true? I know the answer is B when X is abundant, the operon is on. But why is this? An explanation would be helpful.

A. when X is abundant, the operon is off B. when X is abundant, the operon is on C. this operon displays repressible, rather than inducible, expression.

D. the mRNA produced by this operon is monocistronic

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3. Assume that in a bacterial species you discover a cluster ofthree genes (A, B, and C) that accountfor the enzymatic production of a cellulose-like carbohydrate (clc)that is needed as a component of its cell wall. When there issufficient clc is in the cell, the three enzymes are notsynthesized. However, when more clc is needed, the three enzymesare abundantly produced. This cluster of genes appears to be undercoordinate control because deletion of a distant gene (R)results in constitutive expression of all three genes even whenexcess clc is present. When mutations (P-) occur in a region upstream ofgene A, no synthesis of the three enzymes occurs even whenclc levels are extremely low. Mutations (O -)that occur right next to the P - mutationsresult in constitutive expression of all three genes even when clcis present at high levels.

(a) Do the three genes (A, B,and C) behave as if they were part of an operon?

(b) What type of control (positive or negative)seems likely to control the production of the three enzymes?

(c) What is the most likely function of theprotein produced from gene R?

(d) Do you expect that clc is an inducer,inhibitor, or corepressor?

(e) You discover that clc binds to the proteinmade from gene R. What is the most likely effect of this binding?(Hint: will it cause the R protein to bind DNA or fall off ofthe DNA?)

(f) Where do you think protein R binds?(Hint: P region or O region ?)

Mutations that introduce stop codons cause a number of geneticdiseases. For example, from 2% to 5% of the people who have cysticfibrosis possess a mutation that causes a premature stop codon inthe gene encoding the cystic fibrosis transmembrane conductanceregulator (CFTR). This premature stop codon produces a truncatedform of CFTR that is nonfunctional and results in the symptoms ofcystic fibrosis. One possible way to treat people with geneticdiseases caused by these types of mutations is to trick theribosome into reading through the stop codon, inserting an aminoacid into its place. Although the protein produced may have onealtered amino acid, it is more likely to be at least partlyfunctional than is the truncated protein produced when the ribosomestalls at the stop codon. Indeed, geneticists have conductedclinical trials on people with cystic fibrosis with the use of adrug called PTC124, which interferes with the ribosome's ability tocorrectly read stop codons (C. Ainsworth, 2005, Nature438:726รขย€ย“728). On the basis of what you know about the mechanism ofnonsense-mediated mRNA decay (NMD), would you expect NMD to be aproblem with this type of treatment?
Yes, NMD would be a problem, as it requires ribosome torecognize a specific stop codon.
Yes, NMD would be a problem because even although the ribosomewould read through the stop codon, premature degradation of themRNA would take place.
None of the above is true.
No, NMD would not be a problem because the ribosome would readthrough the mutated stop codon, removing exon-junction proteinsthat would normally signal premature degradation of mRNA.
No, NMD would not be a problem because it only occurs inprokaryotes.

1). Thyroid hormone (TH) has been identified as one of the factors promoting phenotype development in the Mexican axolotl salamander. Which of the following statements regarding the impact of TH is FALSE?

A). Axolotls maturing in water with high concentration of TH (thyroxine; T4) metamorphose into a terrestrial form.

B). A genome-wide scan of both the axolotl and its sister species found a large reduction in the number of mRNA transcripts that regulate the production of TH.

C). Adding TH (thyroxine; T4) to the water in which axolotl individuals are reared causes them to remain in a larval stage.

D). Most salamander species produce a burst of TH when they move from water to land.

2).What would be an appropriate evolutionary explanation of the fact that the ordering of some homeotic genes (such as Hox genes) on vertebrate chromosomes parallels the ordering of homeotic genes on fruit fly chromosomes?

A). The similarity is a coincidence, not documented in other invertebrates and largely a result of random mutations.

B). Homeotic genes show that insects and vertebrates are closer relatives than the traditional classification system indicates.

C). Homeotic genes of different animal lineages might be ordered in a similar fashion, yet their sequences are completely different.

D). The similar ordering of homeotic genes in animals, both vertebrate and insect, is due to ancient homology.

3). Which of the following correctly defines "homeotic genes"?

A). Homeotic genes encode proteins that control the cellular environment in a differentiated cell tissue.

B). Homeotic genes are DNA sequences that turn off, but not on, the expression of other genes and are controlled by "master-switch" genes.

C). Homeotic genes are "master-switch" genes that control other genes in a set sequence and thereby affect cell size, shape, division, and the positioning of the cells within the organism.

D). Homeotic genes are DNA sequences that turn on, but not off, the expression of other genes and are controlled by "master-switch" genes.

4). Which of the following is NOT considered a type of heterochrony (change in the rate and timing of development)?

A). hypermorphosis

B). acceleration

C). neoteny

D). ontogeny

5). How does the dominance theory explain why the heterogametic sex is at a disadvantage in Haldane's rule?

A). Beneficial dominant alleles will never be fully expressed in hybrids as they only carry one copy of the sex chromosome that carries the allele.

B). If a dominant allele has a negative effect on the fitness of hybrids, it will always be expressed in the heterogametic hybrids that possess that allele because they only need one copy of the respective sex chromosome.

C). If a recessive allele linked to a sex chromosome has a negative effect on the fitness of hybrids, that allele will always be expressed in the heterogametic hybrids that possess that allele because they only have one copy of the sex chromosome that carries the allele.

D). If a recessive allele linked to a sex chromosome has a positive effect on the fitness of hybrids, that allele will never be expressed in the heterogametic hybrids that possess that allele because they only have one copy of the sex chromosome that carries the allele.

6). In a hypothetical flowering plant species, one population evolves a different response to environmental stimuli and begins to bloom significantly later in the season than nearby populations. What type of reproductive isolating mechanism would this be?

A). hybrid sterility

B). postzygotic

C). prezygotic

D). gametic incompatibility

7). In a study of red spruce trees and black spruce trees, scientists found that the red spruce was living in a smaller geographic area and had much less genetic variation than the black spruce. They proposed that the red spruce might have arisen from a southern population of black spruce, which became geographically isolated from other black spruce populations at some point during the Pleistocene glaciations. What is this an example of?

A). allopatric speciation with the vicariance model

B). sympatric speciation

C). allopatric speciation with the peripheral isolate model

D). sympatric speciation with the ring species model

8). Which of the following defines Haldane's rule and its predictions?

A). If among hybrid offspring one sex is absent, rare, or sterile, that sex is always male.

B). If among hybrid offspring one sex is absent, rare, or sterile, that sex is always female.

C). If among hybrid offspring one sex is absent, rare, or sterile, that sex is heterogametic (has two different sex chromosomes).

D). If among hybrid offspring one sex is absent, rare, or sterile, that sex is homogametic (has two of the same sex chromosomes).

8.) Which of the following statements best explains secondary reinforcement?

A). If the reproductive isolating mechanisms that developed during the geographic isolation are strong but the hybrids have higher fitness than the parent species, then the speciation process will cease.

B). If the reproductive isolating mechanisms that developed during the geographic isolation are somewhat weak but the hybrids between two populations have lower fitness, then the speciation process may continue.

C). If the reproductive isolating mechanisms that developed during the geographic isolation are sufficiently weak as to allow free interbreeding across reunited populations, then the speciation process will halt and a single species will remain.

D). When geographic isolation comes to an end, two populations always complete the divergence process and become separate species.

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