Reading Genes & DNA Content Science by Richard Walker DNA Fingerprinting Reading Strategy Question the Author What is the author trying to say here? This “ordinary” fingerprint is made up of a unique pattern produced by ridges on the fingertips Our fingertips are covered with tiny ridges that leave behind sweaty patterns—fingerprints—when we touch things Individual fingerprints are unique and not shared with anyone else Police can use fingerprints left at the scene of a crime to identify and convict criminals Today detectives have a more sophisticated way of catching crooks—by identifying their unique DNA “fingerprints.” Gathering evidence Whoever robbed this office thought they were being smart By wearing gloves they left no fingerprints But a specially trained police officer discovered something interesting As the thief left, his or her head snagged against the broken window, pulling out some hairs The police officer carefully collected the hairs and sent them to a forensic laboratory There scientists extracted the DNA from cells in the base of the hairs to make a DNA fingerprint that would pinpoint one of three people under suspicion A broken window, disturbed office furniture, and stolen belongings The thief has long since left this crime scene But has he or she left behind any traces that can be used for DNA fingerprinting? sophisticated complex, advanced snagged caught on something forensic related to scientific methods to get information about a crime extracted removed, pulled out pinpoint locate exactly under suspicion thought to be guilty traces hints of evidence 154 Unit • Chapter Making a DNA fingerprint A strand of hair provides the vital evidence in this crime Cells taken from the hair roots are used to prepare a DNA fingerprint that can be compared with the suspects’ DNA The three percent of our DNA involved with building our bodies is virtually the same in all of us But the remaining 97 percent has sections that vary a lot between people These sections consist of stretches of DNA code that repeat themselves between five and 1,000 times and are dotted throughout the genome The number of repeats in each of these sections, and therefore its size, varies a lot from one person to another Scientists can break up a person’s DNA, pick out the repeated sections, and separate them by size to produce a special photograph that looks like a bar code This DNA fingerprint is unique for that person Conclusive proof? So who broke into the office? Take a look at the evidence presented below and match the DNA fingerprint produced from the hair sample with one of the suspects’ DNA fingerprints The evidence is conclusive—it was the man in the top photo Or is it? Not if he has an identical twin with an identical genome But otherwise there is only a minuscule chance that someone else would have the same DNA fingerprint DNA fingerprinting has solved many real-life crimes, resulting in the conviction of criminals and proving the innocence of people who have been wrongly accused Forensic scientists, seen here examining DNA fingerprints, specialize in examining evidence from crime scenes in order to help police arrest and convict criminals Using modern techniques, they can extract enough DNA to make a fingerprint from only a tiny flake of skin, a drop of blood, or a drop of saliva Reading Strategy Question the Author These suspects have been arrested A police doctor has taken blood samples from each one of them Forensic scientists have used cells from the blood to produce DNA fingerprints Here each DNA fingerprint is shown next to the suspect it belongs to, with the fingerprint from the hair found at the crime scene next to each for comparison genome an organism’s complete set of DNA minuscule the tiniest conviction finding someone guilty of or at fault for a crime in a court of law innocence lack of guilt or fault accused charged with wrongdoing vital most important specialize study and work in a specific subject saliva liquid in the mouth that helps us chew food How does this connect with what the author told us before? ✓ Reading Check Recall detailsWhy the police look for fingerprints at a crime scene? InferWhat is a “DNA fingerprint”? Unit • Chapter 155 Genetic Fingerprinting Reading Strategy Question the Author Why you think the author tells us this now? The development of DNA testing, or genetic fingerprinting, has had a significant impact on the field of forensic science Minute samples of blood and other bodily fluids, as well as hair, skin, and fibers, can enable scientists to determine the most likely suspect in a case with amazing accuracy The process involves taking, for example, samples of blood (1), from which DNA can be extracted (2) Each strand of DNA is isolated (3) and chemically sliced into fragments and radioactively labeled (4) These fragments of DNA (5) are placed on a sheet of polymer gel and separated by electrophoresis The sheet is then covered by an X-ray plate (6) Different plates, for the suspects, victim, and any evidence found at the scene of the crime (7) are checked against each other to see if any match genetic of or related to genes minute very small radioactively by radiation (heat and light) polymer gel an artificial substance electrophoresis a process for breaking apart substances 156 Unit • Chapter ... blood (1), from which DNA can be extracted (2) Each strand of DNA is isolated (3) and chemically sliced into fragments and radioactively labeled (4) These fragments of DNA (5) are placed on a...Making a DNA fingerprint A strand of hair provides the vital evidence in this crime Cells taken from the hair roots are used to prepare a DNA fingerprint that can be compared with the suspects’ DNA. .. Scientists can break up a person’s DNA, pick out the repeated sections, and separate them by size to produce a special photograph that looks like a bar code This DNA fingerprint is unique for that