DNA as Evidence From the book DNA in the Courtroom. Advances were made during the 1930s in discovering new blood types such as the Rh factor and again in the 1970s with the invention of electrophoresis, a new method for separating and identifying some of the variable proteins found in blood that are the keys to classic genetic typing.
Proteins comprise the majority of the structural and functional substances that make up our bodies.
Application of more and more of these typing systems allowed an increasing percentage of the wrongly suspected individuals to be excluded as the source of an evidence stain. A major problem with the classical systems that test proteins found in blood, is that very few of these proteins are also found in semen and other body fluids. Because the majority of cases that require genetic typing are sexual assaults, the lack of a definitive set of useful genetic markers in semen has long been a great handicap to the scientific analysis of rape evidence. DNA is found in almost every cell in the body. DNA typing has greatly expanded the sources of evidence that can be tested, while simultaneously reducing the amount of evidence necessary to perform a conclusive test.