Question

1. Which vector would be best suited for constructing a human genomic library with the largest sized insect fragment?

a) Plasmid b) T4 phage   c) Lamda phage   d) YAC e) BAC

2. Successfully cloning an insert into a vector results in the production of a recombinant molecule. Name three enzymes that are commonly required for high efficiency of cloning.

3. A trait that is expressed in only one sex even though the trait may not be sex linked is reffered to as __________ inheritance.

4. Restriction endonucleases naturally occur in bacteria. A)What is the natural (biological/biochemical) function of restriction endonucleases? B) How do bacteria avoid the effects of restriction endonucleases?

Answer 1

1. the BAC vector is used for this purpose. Although YAC vector can have similar or larger inserts there is a problem with clonal stability and chimerism and also in isolation of intact YAC DNA, which the BAC vector does not possess and BACs can accommodate DNA fragments of 18-200kb, so BAC is used(option e)

2. The enzymes used in the process of cloning are-

DNA polymerase- to obtain from primers and increase the copy number of the gene to be inserted in the vector.

Restriction endonucleases- to digest the vector as well as the insert and create compatible ends for ligation into the vector.

DNA ligase- To ligate the compatible ends of the PCR product of the insert and the vector and thus ensure that a recombinant DNA molecule has formed containing a gene insert from a different source that has been put in the vector for cloning.

3. It is called imprinted inheritance. in this pattern of inheritance, there is involvement of epigenetics like DNA methylation and the genes are expressed in a parent of origin-specific way. alleles of particular genes are imprinted in one parent and not imprinted in the other and is thus expressed.

4.A) In bacteria the role of restriction enzyme is a defense against viruses that invade the bacteria and remain as a bacteriophage. the enzymes have recognition sites on the viral genome that allow them to digest and thus degrade the viral genome.

B) The sites recognized by the bacteria to digest the viral genome might also be present in the bacterial counterparts that do not integrate the bacteriophage. these sites are made unrecognizable by the enzymes by modifying them by DNA methylation in the bacterial genome, so that the enzymes do not cleave its own genome. A DNA modification proficient bacterial genome is thus not cleaved by the restriction endonucleases.