Bacterial Genetics (GATE - XL)

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.

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.

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

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.

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.

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 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.

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

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

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

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.

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

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 horizontal gene transfer. It plays an important role in the evolution of bacteria that can degrade novel compounds.

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.