B.3.1_Genes and DNA

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

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

Genes & DNA

Question the Author

What is the author

trying to say here?

Reading

Strategy

This “ordinary” fingerprint is

made up of a unique pattern

produced by ridges on the

fingertips.

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?

DNA Fingerprinting

1 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

2 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.

Content

Science

Reading 2

by Richard Walker

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

Question the Author

How does this connect with what the author told us before?

Reading Strategy

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.

Making a DNA fingerprint

3 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?

4 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.

Reading Check ✓

1 Recall details Why

do the police look for fingerprints at

a crime scene?

2 Infer What is a

“DNA fingerprint”?

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

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.

1 2

3 4

7

Genetic Fingerprinting

5 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

6 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

Question the Author

Why do you think the

author tells us this

now?

Reading

Strategy