1. A plasmid vector and chromosomal DNA are treated separately with the same restriction enzyme.

Which of the following might occur if the digested plasmid and chromosomal DNA were incubated together?

A. The two sticky ends of the plasmid could hybridize back together, recircularizing.
B. The two sticky ends of the plasmid could hybridize to both sticky ends of the chromosomal DNA fragments.
C. The two sticky ends of the plasmid could hybridize back together and recircularize as well as hybridize to both ends of a fragment of chromosomal DNA.
D. The two sticky ends of the plasmid could hybridize with two ends of another type of plasmid.
E. The two sticky ends of the vector would remain free or unhybridized.


4. A researcher uses a probe complementary to the gene of interest and performs a colony hybridization experiment on a plate containing many bacterial colonies. Each bacterial colony contains a recombinant vector with a different piece of chromosomal DNA. What can be learned from this experiment?

A. The researcher can determine the level of expression for each gene represented.
B. The researcher can identify colonies that contain the gene of interest.
C. The researcher can identify colonies that have not taken up a vector.
D. The researcher can determine the amount of mRNA in a specific colony.
E. The researcher can determine the amount of DNA in each of the colonies

For number 1 both A and B will occur unless additional steps are taken to prevent A such as dephosphorylating the plasmid ends. Otherwise conditions can be adjusted to favor B which is generally the desired outcome such as using an excess of the chromosomal DNA.

For number 4 the answer is B. The probe is complementary to the gene of interest so that only colonies with that sequence will bind the probe which allows the colony to be identified.

I agree with Paul, but here the expected answer must be C (corresponding to both A and B occuring)