DNA FingerprintingDNA is the genetic material found within the cell nuclei of all livingth

DNA Fingerprinting

DNA is the genetic material found within the cell nuclei of all livingthings. In mammals(哺乳动物)the strands of DNA are grouped into structures called chromosomes(染色体). With the exceptionof identical twins, the complete DNA of each individual is unique.

DNA fingerprinting is sometimes called DNAtyping. It is a method of identification that compares bits of DNA. A DNAfingerprint is constructed by first drawing out a DNA sample from body tissueor fluid such as hair, blood, or saliva(唾液). The sample is then segmented using enzymesc酶) , and the segmentsare arranged by size. The segments are marked with probes and exposed on X-rayfilm,where they form. a pattern of black bars-the DNA fingerprint. If the DNAfingerprints produced from two different samples match, the two samplesprobably came from the same person.

DNA fingerprinting was firstdeveloped as an identification technique in 1985. Originally used to detect thepresence of genetic diseases, it soon came to be used in criminalinvestigations and legal af-fairs. The first criminal conviction based on DNAevidence in theUnited Statesoccurred in 1988. In criminalinvestigations, DNA fingerprints derived from evidence collected at the crimescene are com-pared to the DNA fingerprints of suspects. Generally, courts haveaccepted the reliability of DNA tes-ting and admitted DNA test results intoevidence. However, DNA fingerprinting is controversial in a number of areas:the accuracy of the results, the cost of testing, and the possible misuse of thetech-nique.

The accuracy of DNAfingerprinting has been challenged for several reasons. First, because DNAsegments rather than complete DNA strands are "fingerprinted"; a DNAfingerprint may not be unique; large-scale research to confirm the uniquenessof DNA fingerprinting test results has not been conducted. In addition, DNAfingerprinting is often done in private Iaboratories that may not followuniform. testing standards and quality controls. Also, since human beings mustinterpret the test, human error could lead to false results.

DNA fingerprinting isexpensive. Suspects who are unable to provide their own DNA to experts may notbe able to successfully defend themselves against charges based on DNAevidence.

Widespread use of DNA testingfor identification purposes may lead to the establishment of a DNA fingerprintdatabase.

If two sisters are identical twins, their complete DNAs are

A.the same

B.unique

C.different

D.similar