How Much Do You Know About Forensic Science?

Humans can have type A, B, AB or O blood. The blood types are further divided up by what sort of antigens the cells carry -- a subject too complex to go into here.

The prefix "hema-" comes from the Greek word "haima," meaning "blood." You'll see it in names of certain tests run on blood.

Bertillon, Herschel and Galton made contributions to anthropometry (body measuring) or fingerprinting in the 19th century. Arthur Conan Doyle was a writer who created Sherlock Holmes, the fictitious character who sometimes used early versions of forensics. However, that doesn't actually qualify as a contribution to the field!

The PCR-STR process was developed by eccentric scientist Kary Mullis. He credited LSD with helping open his mind to new ways of thinking about science. (Disclaimer: He has since become an AIDS denialist, a climate-change denialist and has reported seeing an alien in the guise of a glowing green raccoon.)

The cheek is easy to access, yet protected from most forms of transfer DNA. An exception might be in the subject has recently been kissing, in which case the other person's cells might have transferred to the subject's mouth (as seen, for example, in the movie "Gattaca."

"Rigor mortis" is Latin for "stiffness of death." Bodies do not remain rigid; the condition peaks about 12 hours after death and then the muscles slowly begin to relax again.

Most people don't share toothbrushes, making them a good source of cellular material. The other objects named above are too readily touched or handled by other persons.

This is a bit of a trick question. Urine is sterile, and does not in itself contain DNA. But urine can carry skin cells from the lining of the bladder, so it's possible to get DNA from urine in that way.

Almost anything can be "forensic," in the dictionary definition of "detailed and minute analysis." But criminal forensic science, as we define it today, doesn't include IQ testing -- that would be done by a psychologist.

Fingerprints are unique, even to identical twins. But both kinds of DNA, autosomal and mitochondrial, are shared by twins. As, of course, is blood type.

A forensic scientist should never be afraid to admit a result is inconclusive. Often, a person's freedom hangs in the balance; the evidence can't be forced to fit a desired outcome.

Livor mortis presents as a bluish color in the lowest points of the body (the back, if the corpse is on its back; the front, if it's on its stomach, and so on). If a body has these patches at higher points, it indicates the body has been moved post-mortem.

Most fingerprints at a crime scene are latent. That why technicians dust for them -- the dust makes them visible, then transferable to a surface for later analysis.

Luminol is a substance that reacts with the iron in hemoglobin. It glows when exposed to that iron, hence its name.

DNA testing is capable of determining family relationships, in which DNA is not identical, but has more points of similarity than that of a stranger. If this were not true, DNA testing couldn't be used to determine the father of a baby.

It's a misconception that only fingerprints have identified suspects. Given adequate imprinting on surfaces, other parts of the body can be used as well.

A void area appears where an object at close range intercepts spurting blood, which can be seen on either side of the void. Often, this object is the killer's body itself. Put more bluntly, if someone slashes another person's throat, there'll be a void area on the wall behind them from where the blood spattered onto the killer's own upper body.

The significance of mitochondrial DNA is that it survives much longer than nuclear DNA (which comes from the nucleus of the cell). Mitochondrial DNA has been used in cold cases like that of Jack the Ripper (though without definitive results).

A "control sample" is like the control in a science experiment: It's the known factor. So if a person is missing, and there's blood at their home, police might take a DNA sample from a full-blood sibling as a "control sample." If the DNA from the blood at the scene is a near-match for that of the sibling, that's conclusive: It's almost certainly the missing person's blood at the scene.

Handguns and rifles have "rifling" in the barrel, a spiral pattern that makes the bullet spin, and thus keep a straighter trajectory. The rifling leaves "grooves" (scraped-away areas) on the slug; "lands" are the unmarked the metal between the grooves. This is how investigators can sometimes match up a slug to the gun that fired it.

Alphonse Bertillon created this system of taking about 20 body measurements to create a nearly unique profile of an offender. It became obsolete with the rise of fingerprinting.

After an piece of evidence -- let's say, a shell casing -- is collected at the scene, documentation is kept of who had it at every point, all the way through to trial. This decreases the chances that someone could tamper with it and not get caught.

Certainly, criminals have thought of this. It doesn't usually work. Much better to wear gloves (though that won't prevent other types of evidence, like hairs and fibers, from being left at the scene).

There are three basic formations in the ridges of a fingerpint: arches, loops and whorls. A "moue" is a petulant expression made with the mouth -- you'll recognize this term if you read vintage novels.

A handwriting sample is called an "exemplar." When blood or DNA is in question, the forensic scientist would ask for a "sample" or "specimen" instead.

Trace evidence can include hairs, fibers, bits of soil and more. How much trace evidence is collected at a scene depends on how thoroughly investigators can go over a scene -- which is, in turn, dictated by departmental resources. Most jurisdictions can't afford to send a battery of technicians to swarm over every crime scene.

Police officers and other investigators usually have fingerprints on file, in case they leave some at a crime scene. Likewise, other people living in a house where a crime took place might be fingerprinted. With these people ruled out, an unknown fingerprint is likely to be that of the criminal.

A fingerprint made in water-soluble paint is transient evidence at a rainy crime scene. Direct sunlight, intense heat or intense cold can also threaten the "half life" of evidence.

"CSI effect" is the increasing tendency of average jurors to expect sophisticated forensics in every case, and to assume that forensic evidence is always 100 percent reliable. Defense attorneys want potential jurors to understand that cases don't hang on forensics alone -- motive still needs to be established, eyewitness testimony heard and so on.

Contamination occurs when evidence isn't treated with proper respect -- for example, if a technician were to handle it with bare hands, getting skin cells or fingerprints on it. It's only tampering if it's deliberate.

Jurors increasingly believe that forensic evidence is infallible. But human error or deliberate tampering with evidence can bring about the wrong result. Limited resources come into play when agencies don't have the funds or personnel to collect enough evidence at a scene. Evidence can't be analyzed if it was never brought to the lab.

A date stamp or timestamp on an email is an example of metadata. Overall, metadata is information that isn't part of a message or content, but tells experts in digital forensics where a message originated, and when and who might have sent it.

Everything organic decomposes, right down to leaves and grass. But the type of decomposition that interests forensic investigators -- specifically, forensic anthropologists -- is human body decomposition.

Patricia Cornwell made this research facility famous when she wrote about it, even naming the book, "The Body Farm," after it. Actually called the University of Tennessee Anthropological Research Facility, it has more than a thousand people pre-registered to donate their bodies to the "farm."

The number of blood stains, clothing fibers and handwriting samples that need examination has remained more or less steady in the last decade. But smartphones and similar technology have created an explosion of video evidence, requiring many more experts who can recover, analyze and authenticate video recordings.