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Correct choice is (a) Homo dimer

Best EXPLANATION: As the ENZYME RECOGNIZES the palindrome sequences, the homodimer would be able to recognize the same sequence from the other end. Thus, RESTRICTION ENDONUCLEASES are homodimers.

The correct answer is (c) This sequence has a probability of occurrence in every 1024 bases

The explanation: The probability of occurrence of an 8 bp recognition sequence can be determined as 4^8, this is because there are 4 bases and 8 SPECIFIC bases in position in this sequence; which is equal to 65536. HOWEVER the rest of the options are true.

Right choice is (d) Lamda phage

Explanation: T PHAGES mainly undergo LYTIC cell cycle, while lamda phages have lysogenic cell cycle. For transduction to occur, the viral genome must INTEGRATE within the nucleoid else it will never incorporate bacterial gene within itself. Thus, only lamda phage will be ABLE to HELP in transduction.

Right ANSWER is (d) Between His^+ and Azi^R

The best EXPLANATION: As the origin of TRANSFER is between His^+ and Azi^R the sequence follows Azi^R, ->Ton^R->Lac^+->His^+ or the reverse direction. Thus, longer TIME is required for His to enter and in most cases before that the conjugation tube breaks.

Right ANSWER is (c) Ribosomally synthesized toxic proteins

For explanation I would say: Bacterocins are ribosomally synthesized proteins or PEPTIDES that are not toxic to the producer but to the other bacteria around it.

Right option is (d) The gene was excised out

Easy explanation: While all the REASONS stand a possibility of being true, under the experimental condition it might be due to the restriction enzyme cleaving out GOI considering it a virus. Thus, the E. coli STRAINS need to be restriction deficient but METHYLATION proficient.

Right answer is (a) Thr Leu AZI

Easiest explanation: Genes Leu and Azi and genes Leu and Thr have a tendency to be incorporated together; this is as a RESULT of their physical PROXIMITY. On the other hand Thr and azi hardy show such tendency so they must be farther apart. This RESULTS in the sequence with Leu in the middle.

Right choice is (b) Met, GAL, Ala

To EXPLAIN I would say: The RECOMBINANT genotype Met+ Ala+ will only result in the case when there is a DOUBLE cross over such that the middle portion is EXCHANGED twice. This is of least occurrence and is deterministic for the sequence.

Correct choice is (d) They may get incorporated in CHROMOSOME

For explanation: Plasmids GENERALLY don’t get incorporated in a chromosome; if it does so then it is KNOWN as episome not plasmids. It is true that plasmids are CIRCULAR, double stranded, extrachromosomal DNA that can confer antibiotic RESISTANCE.

The CORRECT option is (B) A specialized transducing phage affects a cell infected by same virus

To elaborate: When the RECIPIENT is already infected by the same virus the COMPLETE genome of specialized tranducing phage is already present. This will produce normal infective virus as well as more specialized transducing infective viruses.

Correct answer is (d) Some COLONIES seen in both arms

The best I can explain: Here the transfer of gene is mainly due to transformation. Although the BACTERIAL cells couldn’t come in physical contact yet their nucleic acids could flow with the liquid to other ARM and it can be INCORPORATED by the bacterial cells in the other arm.

The correct ANSWER is (B) SN2

For explanation I WOULD SAY: The reaction is by hydrolysis of the phosphodiester bond between two sugar residues by a nucleophilic attack. Inverted product configuration shows that the substrate was inverted only once. As only bimolecular nucleophilic reaction causes only one time inversion so that is the correct option.

The correct CHOICE is (a) True

Explanation: Pilli forming gene PILUS gene is responsible for forming the cytoplasmic bridge pilli between the two BACTERIA. Without this the plasmid couldn’t be transferred to the other bacteria. Thus, it is REALLY indispensible.

Right answer is (d) Col plasmid

To EXPLAIN I WOULD say: Col plasmids help in the production of cilicins and bacteriocins. This HELPS them to KILL other bacteria. While F plasmids confer fertility and R confers RESISTANCE to some antibiotics.

Right choice is (b) The genes are LINKED

For explanation I would say: The PROBABILITY of incorporation of both should be theoretically 0.2X0.1= 0.02. But experimentally it is found to be 0.1 which is the same as that of 2^nd GENE. Thus these genes are completely linked i.e. WHENEVER b is incorporated a is incorporated as well.

Correct answer is (b) Chloranphemicol resistance

Easy EXPLANATION: The R agent class of plasmids consists of Resistance transfer factor RTF as well as Resistance GENE R. While the origin of REPLICATION and transfer, and pilli forming gene are part of RTF; ANTIBIOTIC resistance gene such as Chloramphenicol resistance gene is part of R.

Right option is (d) CCAGG

Easy explanation: DCM methylates at the C base while DAM methylates at the A base. DCM methylates TA the internal C of the sequence CCAGG. The sequence CCGTT is not a palindrome and GATC is recognized and methylated by DAM.

Correct option is (a) Specialized transduction is due to excision error

To explain I WOULD SAY: When the Lysigenic virus ENTERS Lytic cycle its gene has to EXCISE out of the bacterial genome. Imperfections in this excision can cause excision of a part of bacterial genome along with the circular VIRAL genes. This results in specialized transduction.

Right choice is (c) Both will have the same genetic composition at the end

Easy explanation: Genetic TRANSFER, mainly by conjugation will result in incorporation of the His+ LEU+ gene in both the STRAINS at the end. Then they can PRODUCE both these amino acids by themselves and grow on minimal media. This is not by EXTRACELLULAR process but by contact.

The correct option is (b) Reduction in free ENERGY

The best explanation: On RESTRICTION endonuclease binding to COGNATE DNA there is a reduction in free energy to a greater EXTENT than that in case of non-cognate DNA. This additional energy is used to distort the sequence and produce a kink.

Right answer is (d) No virulence

The BEST explanation: This is because some PART of the viral genome is compromised for this improper EXCISION making it specialized transducing phage. WITHOUT the complete viral genome, the RESULTANT viruses will not be able to express their infective activity.

Right option is (d) Met and Gal only

For explanation: Att site is merely NECESSARY for incorporation of the VIRUS. In specialized transduction the SITES directly beside the attachment point of the virus can be mistakenly excised with the part of viral gene. Here this PHENOMENON will occur only in CASE of Met and Gal.

Right answer is (c) TETRACYCLIN

Explanation: Tetracyclin resistance is provided by some transporters that selectively TRANSPORT tetracycline OUTSIDE the cell thus providing resistance; WHEREAS the other antibiotics are through other MODES of resistance.

Correct answer is (a) F factors

For explanation: EPISOMES are the plasmids that can GET INCORPORATED in a central chromosome. F factors or FERTILITY factor is one such plasmid.

Correct choice is (a) True

Explanation: The methylated bases can bind to the enzyme but it will not be CUT by the enzyme. THUS it can EFFECTIVELY as a competitive inhibitor as it competes with the non-methylated DNA for the same BINDING SITE.

The CORRECT ANSWER is (d) HFR and F+

Easiest explanation: For conjugation to take place one bacterium must have the F PLASMID and other should lack it. HFR has the COMPONENTS of F plasmid within its genome so it can’t mate with another F+.

Correct choice is (d) S PHASE

For explanation I would SAY: In the S phase there is a lot of competition between the BACTERIAS for space and resources. Bacteriocins are USED to kill off the bacterias of same SPECIES or related bacteria to resuce the competition.

The correct answer is (C) By electroporation

The explanation: Electroporation is a TECHNIQUE where a short pulse F ELECTRICITY is used to induce artificial competence in some cells. Treating with chitinase or penicillin will SEVERELY affect the cell wall and the cells will die.

Correct OPTION is (c) SMAI and XmaI

Best EXPLANATION: Neo-isoschizomers are the enzymes that RECOGNIZE the same sequence and cleave at different points. Here, both SMA1 and Xma1 recognize GGGCCC; the 1^st cleaving after the 3^rd G and 2^nd cleaving after the 1^st.

The correct answer is (c) a X b

Easiest explanation: For both GENES to be incorporated together we must MULTIPLY the PROBABILITY of incorporation of either genes. Thus, the probability value overall DECREASES.

Right choice is (d) 1^st stain will not GROW in leu absent media

To explain I WOULD say: In this case, the 1^st strain will have the ability to make leu as it is leu+. So it can grow in leu+ media. The ability of the mixture to grow in minimal media is DUE to the fact that GENE transfer has TAKEN place.

Correct answer is (d) 1000bp AWAY from the recognition sequence

To explain: Type I restriction ENDONUCLEASES are of very less practical UTILITY, this is because although they recognize a particular sequence, they cut the DNA up to 1000bp away not PROVIDING much specificity.

Right ANSWER is (c) Panthera sp

For explanation: Among the FOLLOWING options only prokaryotes and lower eukaryotes like yeast can have PLASMIDS. So option a and d being prokaryote and b being yeast has PLASMID. But option c being higher eukaryote i.e. the genus of tiger lacks plasmids.

The correct ANSWER is (a) SINGLE crossover event

The best I can explain: A viral GENOME is INTRODUCED in bacteria as a circular plasmid. It will be incorporated by a single cross over between the att site of virus and the att Lamda site of bacteria.

Right option is (B) o P r

Easy explanation: This is because o and p have an APPRECIABLE degree of co-incorporation, as does r and p but o and r have much lower degree of co-incorporation. This SHOWS that p must be at the middle of o and r.

The correct OPTION is (b) A variety of GENES can be transformed in this case

For explanation I WOULD say: Here the viral genome is actually incorporated in the bacterial genome at a particular site. The virus can transfer the GENE surrounding its recombination site only. It is certainly through lusogenic cycle which is seen in lamda phages INCLUDING K12.

Right choice is (C) Gal

To explain: Gal can be incorporated alone only by the EVENT of double cross over. Double crossover at such SHORT STRETCH is of least OCCURRENCE so the probability of it being incorporated alone is least.

The correct option is (b) F-

Explanation: In HFR rarely the complete chromosome can be transferred from ONE bacterium to other DUE to the continuous motion of the medium. Here only partially the GENES from Ori of transfer till the point where conjugation channel is broken gets transferred. As the full F plasmid can THUS never be transferred so it is F-.

Correct choice is (c) SEX determining gene

The best I can explain: There is no particular sex determining gene in bacteria, their pseudo sex is determined by presence or absence f FERTILITY FACTOR. HOWEVER pilli forming gene is necessary for the conjugation channel, ORI of transfer and ori of replication also maintain a plasmid.

Right choice is (d) Streptococcus pneumoniae

Easy EXPLANATION: Only 1% of all the bacterial STRAINS are naturally competent. One among these is Streptococcus pneumonia, which can TAKE up the chromosomes from the MEDIUM without prior treatment.