Question

1. The substrate used for blue-white screen is called:
   1. B-galactosidase.
   2. X-gal.
   3. Ampicillin.
   4. Blue colony.
2. The Ti plasmid is:
   1. A conjugation plasmid.
   2. Used for transfer of genes between bacteria and plant cells.
   3. Encodes genes that force plant cells to produce products that are beneficial to the bacteria.
   4. All of the above.
3. During Southern blotting, describe the difference between migration and separation of DNA fragments.

Answer 1

The substrate used for blue-white screen is called x-gal. X-gal or 5-bromo-4-chloro-3-indolyl-β-D-galacto-pyranoside is broken down by β-galactosidase enzyme into galactose and 4-chloro-3-brom-indigo (insoluble blue pigment).

Ti plasmids code for functions associated with i) plasmid replication and maintenance, ii) conjugative transfer, iii) virulence, iv) opine utilization, and v) sensory perception of exogenous signals released by the plant host and neighboring agrobacterial cells at the site of infection

The function of all Ti plasmid is that

a) It codes for the maintenance and replication of the plasmid

b) Helps in conjugative transfer

c) Codes for virulence

d) codes for utilization of opine

Therefore all the above options are true.

In southern blotting when the DNA is placed under the electric field, the fragments migrate towards the anode (positively charged). The fragments get separated on the basis of the size ( smaller moves farther and larger travels shorter distance. Then the DNA can be seen under Uv light after staining them with dye.

Migration is the movement of DNA and separation in the end result of the migration.