The Norway rat (Rattus Norvegicus), a widespread pest, was controlled for about a decade by the anticoagulant warfarin. This chemical substance, placed in food pellets, is absorbed by the intestinal tract and inhibits the clotting of blood. After a population decline for about 10 years, rat populations increased and stabilized. In one European population, as illustrated in the graph below, the percentage of rats resistant to warfarin has remained fairly stable over a number of years.

Resistance to warfarin is governed by a dominant autosomal gene, R. More than 15 percent of the resistant animals are heterozygous at this locus (Rr). The table below indicates the response to warfarin and relative reproductive fitness of individuals that are homozygous or heterozygous for the dominant gene (R). The RR individuals have a 20-fold increase in vitamin K requirement over individuals.

Fitness is a measure of the reproductive success of a particular genotype. The highest fitness is 1.00.

There is a substantial number of heterozygotes in the population. Which of the following is the best explanation of this observation?

#Question id: 1530

#Unit 4. Cell Communication and Cell Signaling

What are the differences and similarities between the transforming genes of retroviruses and those of DNA tumor viruses?

#Question id: 1529

#Unit 4. Cell Communication and Cell Signaling

Which of the following statements are true regarding to gain-of-function and loss-of-function mutations with respect to cancer.

#Question id: 1528

#Unit 4. Cell Communication and Cell Signaling

Mutation of p53 is described as a dominant-negative mutation. Which of the following statement is correct regarding to the mechanism by which this mutation causes the dominant-negative phenotype?

#Question id: 1527

#Unit 4. Cell Communication and Cell Signaling

Following are the six fundamental properties of malignant tumors. Which of these properties are amenable to study in a cell culture model of cancer?

(I) self-sufficiency in growth signals

(II) insensitivity to antigrowth signals

(III) evasion of apoptosis

(IV) limitless replicative potential

(V) sustained angiogenesis

(VI) tissue invasion and metastasis

#Question id: 1526

#Unit 4. Cell Communication and Cell Signaling

Following statements are regarding to apoptosis.

A. In the worm apoptotic pathway, CED-3 (caspase-9 in mammals) is a protease required to destroy cell components during apoptosis.

B. CED-4 (Apaf-1) was able to accelerate the autoproteolytic cleavage and activation of purified CED-9

C. Once EGL-1 causes dissociation of the CED-4/CED-9 complex, the released CED-4 dimer joins with three other CED-4 dimers to make an octamer, which then activates CED-3

D. Many apoptotic stimuli lead to damage of the outer mitochondrial membrane, causing release into the cytosol of several proteins that stimulate apoptosis. In particular, cytochrome c released from mitochondria activates Apaf-1, which in turn activates caspase-3 and 7.

Which of the following combination is incorrect?

#Question id: 1525

#Unit 4. Cell Communication and Cell Signaling

Following statements are regarding to chromatin remodelling factors SWI/SNF complexes. Which one of them is incorrect?