DNA Fingerprinting？？ DNA isthe genetic material found within the cell nuclei of all living

DNA Fingerprinting

？？ DNA isthe genetic material found within the cell nuclei of all living things. Inmammals the strands of DNA are grouped into structures called chromosomes. Withthe exception of identical sib- lings (as in identical twins) , the completeDNA of each individual is unique.

？？DNAfingerprinting is somet？？imes called DNA typing. It is a method of identificationthat compares bits of DNA. A DNA fingerprint is constructed by first drawingout a DNA sample from body tissue or fluid such as hair, blood, or saliva. Thesample is then segmented using enzymes, and the segments are arranged by size.The segments are marked with probes and exposed on X-ray film, where they forma pattern of black bars-the DNA fingerprint. If the DNA fingerprints producedfrom two differ- ent samples match, the two samples probably came from the sameperson.？？

？？DNAfingerprinting was first developed as all identification technique in 1985.Originally used to detect the presence of genetic diseases, it soon came to beused in criminal investigations and legal af- fairs. The first criminal convictionbased on DNA evidence in the United States occurred in 1988. In criminalinvestigations, DNA fingerprints derived from evidence collected at the crimescene are com- pared to the DNA fingerprints of suspects. Generally, courtshave accepted the reliability of DNA tes- ting and admitted DNA test resultsinto evidence. However, DNA fingerprinting is controversial in a number ofareas:the accuracy of the results, the cost of testing, and the possible misuseof the tech-nique.

？？ Theaccuracy of DNA fingerprinting has been challenged for several reasons. First？？,because DNA seg-ments rather than complete DNA strands are"fingerprinted": a DNA fingerprint may not be unique; large-scaleresearch to confirm the uniqueness of DNA fingerprinting test results has notbeen conducted. In addi-tion, DNA fingerprinting is often done in privatelaboratories that may not follow uniform. testing standards and qualitycontrols. Also, since human beings must interpret the test, human error couldlead to false re-sults.

？？ DNA fingerprinting is expen？？sive. Suspectswho are unable to provide their own DNA to experts may not be able tosuccessfully defend themselves against charges based on DNA evidence.

？？ Widespread use of DNA testing for identification purposes may lead tothe establishment of a DNA fingerprint database？？.？？

？？ According to the essay, we can findchromosomes ________？？

A.in a fish

B.in a tree

C.in a sheep

D.in a rock