cDNA

Researchers can make another kind of DNA library by starting with mRNA extracted from cells.
The enzyme __(obtained from retroviruses) is used in vitro to make single-stranded DNA transcripts of the mRNA molecules.
The __allows use of a short strand of __as a primer for the __.

Following enzymatic degradation of the mRNA, a second DNA strand, complementary to the first, is synthesized by __.
· The resulting double-stranded DNA is called __.

For creating a library, the __is modified by the addition of __at each end. Then the __is inserted into vector DNA in a manner similar to the insertion of genomic DNA fragments.

The extracted mRNA is a mixture of all the mRNA molecules in the original cells transcribed from many different genes. Therefore, the __that are cloned make up a __containing a collection of genes.

However, a __represents only part of the genome-only the subset of genes that were transcribed in the cells from which the mRNA was isolated.