291.

Two groups (Control, Treated) are to be compared to test the effect of a treatment. Since individual variability is high in both groups, the appropriate statistical test to use is

• Analysis of variance

• Kendall's test

• Student's t-test

• Mann-Whitney U-test

When one isolates ribosomes from bacterial lysate, apart from 70S, 50S and 30S ribosomal subunits, one also finds a small population of 100S, 130S and 150S sub-units. EDTA dissociated these larger ribosomal subunits into 50S and 30S, suggesting that they have both the subunits. Upon addition of cations, they reassociate into 70S, but none of the other forms could be detected. What is the reason for not obtaining the >70S forms?

• The effects of EDTA cannot be reversed by the addition of cations.

• 100S, 130S and 150S are modified form of ribosomes that are irreversibly damaged by EDTA.

• 100S, 130S, etc. represent polysome that cannot be reassembled denovo without other components.

• They are obtained as an experimental artifact in preparations of ribosomes.

A researcher was studying a protein 'X' which has been observed to move across cells when an extracellular electrical stimulus is provided. An artificial peptide 'P' was prepared which resembles the structure of connexins and competitively inhibits connexion formation. Which one of the following statements will best explain the fate of protein 'X' if the cells are treated with peptide 'P' and then electrical stimulus is provided.

• X fails to move across cells due to improper formation of tight junctions.

• X fails to move across cells due to improper formation of gap junctions.

• X moves freely across cells as before.

• X fails to move across cells due to improper formation of desmosomes.

A plant with red fruit is crossed to a plant with white fruit. The F₁ progeny had red fruits. On selfing the F₁, the two kinds of progeny were observed, plants with red-fruits and those with white-fruits. To test whether it was a case of recessive epistatic interaction a chi-square test was performed. A value of 1.062 was obtained (chi-square value at P_0.05 = 3.841 for Degree of Freedom = 1). The following statements were made:

A. The null hypothesis was that plants with red and white fruits will occur in a 9 : 7 ratio.

B. The null hypothesis was that plants with red and white fruits will occur in a 1 : 1 ratio.

C. Based on the chi-square value, it is a case of recessive epistatic interaction.

D. Based on the chi-square value, it is not a case of recessive epistatic interaction.

Which of the combination of above statements is correct?

• A and C

• A and D

• B and C

• B and D

Homing pigeons, when released at a place far away from their home, use earth's magnetic field or the sun as navigational cues and choose the right direction to fly. To test the hypotheses, two experiments were conducted. In Expt I, one group of pigeon (Test) were equipped with Hemholtz coils (which disrupt magnetic field detection), while the second group (Control) were not. Both groups were released on a sunny day. Expt II used the same Control and Test groups of pigeons, but they were released on a cloudy, overcast day. The expected results, if the hypotheses is true, would be 

• In Expt. I, both Control and Test groups fly in the right direction, but in Expt. II only Control group does.

• In both experiments, test groups fail to choose the right direction.

• In Expt. I and II, Test groups fly in the right direction.

• In Expt. I both groups fly in the right direction but in Expt. II both groups fail to choose the right direction.

A gene from genomic library is screened by using hybridization technique. After hybridizing the probe, usually a stringent washing step is given. The following statements are given to explain the stringent washing step:

A. Stringent washing takes care of removing unincorporated and non-specifically hybridized probe molecules.

B. Stringent washing is done in solution having high salt concentration and lower temoerature.

C. Stringent washing is done in solution having low salt concentration keeping higher temperature.

D. Salt present in washing solution supports hybrids to stay intact by shielding the interference of water molecules.

E. Salt reacts with DNA molecules and allows easy dissociation of hybrids.

F. Stability of hybrid is directly proportional to the temperature.

Which combination of the above statements is most appropriate for stringent washing step?

• A, B and D

• A, C and D

• A, B and F

• C, E and F

A student, while constructing knock-out mice, isolated mouse embryonic stem cells and introduced an engineered DNA into the cells. However, none of the mice were transgenic. On checking the cells containing DNA construct, he found that he had made a mistake in constructing the DNA since the cells were resistant to gancyclovir but sensitive to G418. Which one of the following constructs had the designed?

The mean and standard deviation of serum cholesterol in a population of senior citizens are assumed to be 200 and 24 mg/dl, respectively. In a random sample of 36 senior citizens, what values of cholesterol (to the nearest whole number) should lead to rejection of the null hypothesis at 95% confidence level?

• above 224

• above 248

• below 176 and above 224

• below 192 and above 208

The most important property of any microscope is its resolution (D) and can be calculated from the formula

D = $\frac{0.61\mathrm{\lambda }}{\mathrm{N} \mathrm{sin\alpha }}$

where D is minimum distance between two distinguishable objects, λ is the wave length of incident light, α is the angular aperture and N is the refractive index of the medium. Given below are several suggestions to improve the resolution of a microscope:

A. decrease the wave length of incident light.

B. increase the wavelength of incident light.

C. use oil which has a higher refractive index.

D. use oil because of its lower refractive index.

Which one is the correct suggestion?

• A and C

• Only B

• Only D

• B and D

In response to a drug, changes in protein levels were examined in a cell line. A pulse chase experiment was performed using ³⁵S labeled methionine. In comparison to untreated samples, the following observations were made : few minutes after stimulation, protein X accumulates and this was followed by reduction in protein Y and Z. The correct interpretation of these observations would be:

• Protein X is a protease that degrades Y and Z.

• Protein X is a transcriptional repressor that controls expression of Y and Z.

• Expression of protein X and loss of Y and Z are unrelated.

• Information is not sufficient to distinguish between the three possibilities stated above.