Editing Complementary DNA (section)

==Applications==
Complementary DNA is often used in [[clone (genetics)|gene cloning]] or as [[gene probe]]s or in the creation of a [[cDNA library]]. When scientists transfer a gene from one cell into another cell in order to express the new genetic material as a protein in the recipient cell, the cDNA will be added to the recipient (rather than the entire gene), because the DNA for an entire gene may include DNA that does not code for the protein or that interrupts the coding sequence of the protein (e.g., [[intron]]s). Partial sequences of cDNAs are often obtained as [[expressed sequence tag]]s.

With amplification of DNA sequences via [[polymerase chain reaction]] (PCR) now commonplace, one will typically conduct reverse transcription as an initial step, followed by PCR to obtain an exact sequence of cDNA for intra-cellular expression. This is achieved by designing sequence-specific DNA primers that hybridize to the 5' and 3' ends of a cDNA region coding for a protein. Once amplified, the sequence can be cut at each end with nucleases and inserted into one of many small circular DNA sequences known as expression vectors. Such vectors allow for self-replication, inside the cells, and potentially integration in the host DNA. They typically also contain a strong promoter to drive transcription of the target cDNA into mRNA, which is then translated into protein.

cDNA is also used to study gene expression via methods such as RNA-seq or [[Real-time polymerase chain reaction|RT-qPCR]].<ref>{{Cite journal |last=Derisi |first=J. |last2=Penland |first2=L. |last3=Brown |first3=P. O. |last4=Bittner |first4=M. L. |last5=Meltzer |first5=P. S. |last6=Ray |first6=M. |last7=Chen |first7=Y. |last8=Su |first8=Y. A. |last9=Trent |first9=J. M. |date=December 1996 |title=Use of a cDNA microarray to analyse gene expression patterns in human cancer |url=https://www.nature.com/articles/ng1296-457 |journal=Nature Genetics |language=en |volume=14 |issue=4 |pages=457–460 |doi=10.1038/ng1296-457 |issn=1546-1718 |pmid=8944026 |s2cid=23091561}}</ref><ref>{{Cite journal |last=White |first=Adam K. |last2=VanInsberghe |first2=Michael |last3=Petriv |first3=Oleh I. |last4=Hamidi |first4=Mani |last5=Sikorski |first5=Darek |last6=Marra |first6=Marco A. |last7=Piret |first7=James |last8=Aparicio |first8=Samuel |last9=Hansen |first9=Carl L. |date=2011-08-23 |title=High-throughput microfluidic single-cell RT-qPCR |journal=Proceedings of the National Academy of Sciences |language=en |volume=108 |issue=34 |pages=13999–14004 |bibcode=2011PNAS..10813999W |doi=10.1073/pnas.1019446108 |issn=0027-8424 |pmc=3161570 |pmid=21808033 |doi-access=free}}</ref><ref>{{Cite journal |last=Hrdlickova |first=Radmila |last2=Toloue |first2=Masoud |last3=Tian |first3=Bin |date=January 2017 |title=RNA-Seq methods for transcriptome analysis |journal=Wiley Interdisciplinary Reviews. RNA |volume=8 |issue=1 |pages=e1364 |doi=10.1002/wrna.1364 |issn=1757-7004 |pmc=5717752 |pmid=27198714}}</ref> For sequencing, RNA must be fragmented due to sequencing platform size limitations. Additionally, second-strand synthesized cDNA must be ligated with adapters that allow cDNA fragments to be PCR amplified and bind to sequencing flow cells. Gene-specific analysis methods commonly use microarrays and RT-qPCR to quantify cDNA levels via fluorometric and other methods.

On 13 June 2013, the [[United States Supreme Court]] ruled in the case of ''[[Association for Molecular Pathology v. Myriad Genetics]]'' that while naturally occurring genes cannot be [[patent]]ed, cDNA is patent-eligible because it does not occur naturally.<ref>{{Cite news |last=Liptak |first=Adam |date=13 June 2013 |title=Supreme Court Rules Human Genes May Not Be Patented |url=https://www.nytimes.com/2013/06/14/us/supreme-court-rules-human-genes-may-not-be-patented.html |url-access=limited |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2013/06/14/us/supreme-court-rules-human-genes-may-not-be-patented.html |archive-date=2022-01-01 |access-date=14 June 2013 |work=[[The New York Times]]}}{{cbignore}}</ref>