Gotcha

by Barbara D'Amato


Leicester University in the UK invented DNA fingerprinting in 1984. Now comes news that they will soon be able to predict the surname of a male suspect from blood, hair, saliva or semen found at a crime scene.

DNA on the Y [male] chromosome is passed down the male line. A study of 2,500 men showed that there was a twenty-four per cent likelihood of two men with the same last name having a common ancestor. However, if the last name was uncommon, the chance of a common ancestor was fifty per cent. With very uncommon names, the chance went as high as seventy per cent.

Sooooo—with a large enough database of Y chromosome DNA, a crime scene analyst will be able to send a hair to the lab and, in whatever time it takes, tell us “This hair is from a man named Fosdick.”

Mitochondrial DNA, mtDNA, is inherited from the mother. Both males and females inherit their mother’s, and the father’s is lost. If a person’s mtDNA mutations are the same as another’s, they have a common ancestor. Comparing a sample to the Cambridge Reference Sample identifies the maternal line. All humans today belong to one of only thirty-three haplogroups or clans, which are ethnically specific. In other words, the lab can look at your mtDNA and tell your ethnic makeup. There are even companies which will test your mtDNA and come with an ancestry portrait—for example Fosdick is 2 per cent East Asian, 10 percent Native American, and eighty-eight per cent European.

Since DNA already tells ethnicity and such things as genetic diseases and physical appearance – Fosdick has brown hair and salt-sensitive hypertension -- and mtDNA reveals ancestry, there will soon be nowhere to hide. As crime writers, until fairly recently we had only to keep our malefactor from leaving fingerprints if we didn’t want to catch him too quickly. More recently we had to deal with DNA, but of course that couldn’t be matched unless the police found the bad guy. Now from a smidgen of blood we know what he looks like. Soon we will know his name.

To the crime writer this is both a challenge and an opportunity, as PRESUMED INNOCENT used an earlier level of forensic analysis to befuddle the reader.

The bar has just been raised.