Final answer:
If 20% of the DNA in a plasmid changes from B-DNA to Z-DNA, the value of the linking number compared to the initial value cannot be determined without more information.
Step-by-step explanation:
The linking number of a DNA molecule describes the number of times the two strands of the DNA double helix are intertwined. When DNA switches from the B-DNA to the Z-DNA conformation, the linking number can change. In this case, if 20% of the DNA in the plasmid changes from B-DNA to Z-DNA, the linking number will be different compared to the initial value.
To determine the exact change in linking number, more information about the specific properties of the B-DNA and Z-DNA conformations is needed. Without this information, it is impossible to determine the value of the linking number compared to the initial value.
When a plasmid has 20% of its DNA change from B-DNA to Z-DNA and then treated with EcoRI and DNA Ligase after returning to a low salt solution, the value of the linking number would remain unchanged. This is because the action of EcoRI and DNA Ligase will restore the DNA's original state before the transition to Z-DNA occurred.
In a molecular cloning experiment where foreign DNA has been degraded by nucleases due to improper storage, you would expect a result of no colonies on the bacterial plate because the foreign DNA is necessary for the cloning to succeed.
Lastly, if an enzyme required for the joining together of Okazaki fragments is mutated, the most likely candidate is DNA ligase, as it is essential for sealing nicks in the DNA during replication and recombination processes.