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Bacterial Genetics (GATE - XL)

Description: Proteins
Number of Questions: 15
Created by:
Tags: conjugation mutation plasmids transposons sexduction Recombination Transposons Types of Mutation Conjugation DNA Repair Selection of Mutants Plasmids
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Homologous DNA sequences exhibit

  1. illegitimate recombination

  2. general recombination

  3. site-specific recombination

  4. replicative recombination


Correct Option: B
Explanation:

Genetic exchange takes place between a pair of homologous DNA sequences in general recombination. These are usually located on two copies of the same chromosome, although other types of DNA molecules that share the same nucleotide sequence can also participate.

SOS repair for repairing mutation errors is used by which of the following?

  1. Pseudomonas aeruginosa

  2. E. coli

  3. Mycobacterium tuberculosis

  4. Bacillus subtilis


Correct Option: B
Explanation:

The process by which E. coli repairs large amount of damage is called SOS repair. This process is not a single discrete mechanism. It involves a large number of responses. The ability to repair pyrimidine dimers, to shut off respiration, to delay septum formation and to induce prophages are a few examples. All the processes are well-coordinated.

Which of the following statements regarding site-specific recombination is true?

  1. This type of recombination commonly occurs between a pair of homologous DNA sequences.

  2. This type of recombination does not require homologous sequences and is utilised by mobile genetic elements that move about chromosomes.

  3. This type of recombination does not require homologous sequences and is important for the integration of viral genomes into bacterial chromosomes.

  4. This type of recombination commonly occurs between a pair of non-homologous DNA sequences.


Correct Option: C
Explanation:

This is true. Site-specific recombination does not require homologous sequences and is important for the integration of viral genomes into bacterial chromosomes.

Which of the following bacterial gene transfer mechanisms transfer(s) the greatest amount of information?

  1. Transformation

  2. Transduction

  3. Conjugation

  4. Transformation and transduction


Correct Option: C
Explanation:

The greatest amount of genetic information is transferred during conjugation because actual physical contact occurs in this process. It makes it possible to transfer large DNA sequences.

Which of the following pieces of information can be derived from interrupted mating experiments?

  1. Recombinant frequency

  2. Mutation frequency

  3. Genomic mapping

  4. Gene sequence


Correct Option: C
Explanation:

Interrupted mating experiments are done to determine genomic maps. It is a technique that is used to map bacterial genes by determining the sequence in which donor genes enter recipient cells. Genes are mapped by disrupting conjugation after specific time intervals.

During conjugation, the products of recA gene are required to

  1. facilitate the entry of donor DNA

  2. inherit the incoming genes by homologous recombination

  3. transfer the donor genes to the host DNA

  4. duplicate the DNA during the transfer


Correct Option: B
Explanation:

Transfer of genes from a Hfr into a F-recipient cell (conjugation) requires the recA gene product because the incoming genes need to be inherited by homologous recombination.

Sentence A: It is a common practice to give two antibiotics simultaneously to treat some diseases. Sentence B: The chance of two mutations in the same cell is the product of the single mutation for each.

  1. Sentences A and B are both incorrect.

  2. Sentence A is correct and sentence B is the right explanation of sentence A.

  3. Sentence A is correct but sentence B is not the correct explanation of sentence A.

  4. Sentence A and sentence B are unrelated.


Correct Option: B
Explanation:

Sentence A is correct and sentence B is the right explanation of sentence A. It is a common practice to give two antibiotics simultaneously to treat some diseases because if the mutation rate to first antibiotic is supposed to be 10-6 and mutation rate to the second antibiotic is 10-8 per cell division, then the probability that both the mutations would occur in the same cell is 10-6 x 10-8 = 10-14 This means that the chance of two mutations in the same cell is the product of the single mutation for each.

Which of the following carry only the genes needed for their own transposition?

  1. Direct repeats

  2. Inverted terminal repeats

  3. Insertion sequences

  4. Transposases


Correct Option: C
Explanation:

An insertion sequence is a small bacterial transposon that carries only the genes needed for its own transposition.

Distributive conjugal transfer is observed in

  1. Escherichia coli

  2. Mycobacterium smegmatis

  3. Agrobacterium

  4. Salmonella typhi


Correct Option: B
Explanation:

Distributive conjugal transfer takes place in Mycobacterium smegmatis. In Mycobacterium smegmatis, all regions of the chromosome are transferred with comparable efficiency.

Which of the following statements regarding insertion sequences is false?

  1. They are capable of moving within a chromosome.

  2. They are capable of moving from one chromosome to another chromosome.

  3. They mediate site specific recombination.

  4. They are implicated in the evolution of R-plasmids.


Correct Option: C
Explanation:

This is false. Insertion sequence elements appear to mediate recombination between non-homologous DNA molecules or sequences.

Which of the following events takes place in triparental mating?

  1. Two donor cells conjugate simultaneously with a host cell.

  2. One bacterial strain assists another in transferring genetic material to a third bacterial strain.

  3. Host cell receives the genetic material from three donor cells.

  4. Integrated plasmid, along with an external DNA, fuses with the host DNA.


Correct Option: B
Explanation:

Triparental mating is a form of bacterial conjugation where a conjugative plasmid present in one bacterial strain assists the transfer of a mobilisable plasmid present in a second bacterial strain into a third bacterial strain. In other words, one bacterial strain helps the another in transferring genetic material to a third bacterial strain.

Which of the following was proved by Luria and Delbruck by fluctuation test?

  1. In bacteria, genetic mutations arise in the absence of selection.

  2. In bacteria, genetic mutations arise in response to selection.

  3. Bacteria never develop resistance to their respective phages.

  4. Mutation can be induced by an external factor.


Correct Option: A
Explanation:

Luria and Delbruck (1943) proved by the fluctuation test that in bacteria, genetic mutations arise in the absence of selection.

Which of the following is the product of bacteriocinogenic plasmids in pseudomonas?

  1. Aureocin A53

  2. Warnerin

  3. Microcin V

  4. Pyocin


Correct Option: D
Explanation:

Pyocin synthesis is directed by the bacteriocinogenic plasmids in pseudomonas. They are active against bacteria.

The transfer of genes between bacteria by conjugation is known as

  1. vertical transfer

  2. lateral gene transfer

  3. horizontal gene transfer (HGT)

  4. sexual gene transfer


Correct Option: C
Explanation:

The transfer of genes between bacteria by conjugation is known as horizontal gene transfer. It plays an important role in the evolution of bacteria that can degrade novel compounds.

Which of the following enzymes is not involved in base excision repair (BER) in bacteria?

  1. Ligase

  2. Polymerase

  3. Relaxase

  4. AP endonuclease


Correct Option: C
Explanation:

Relaxase enzyme creates a nick in one of the strands of the conjugative plasmid at the oriT during conjugation. Thus, it is not involved in excision repair in bacteria.

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