Image source: Edelson, Edward. Francis Crick and James Watson and the Building Blocks of Life. Oxford UP, 1998. View Source

The Double Helix

James Watson and Francis Crick did not discover DNA, the primary molecule of inheritance. Deoxyribonucleic acid (DNA) was first identified by Swiss chemist Friedrich Miescher in 1869. Although scientist began to realize DNA importance in transmitting genetic information, it took nearly a century to discover its structure.

In 1953, Watson and Crick, working in the Cavendish Laboratory at Cambridge University, published their landmark article on the double-helical structure of DNA. Aided significantly by X-rays taken by Rosalind Franklin and Maurice Wilkins at Kings College, the Watson-Crick structure is formed by complementary strands connected by hydrogen bonds. This shape, they noted, “suggests a possible copying mechanism for the genetic material.”

Forensic DNA testing can help confirm a suspect’s guilt or, just as important, exclude a suspect from prosecution. In this image from a sexual assault case, Suspect 1’s DNA pattern is a match with DNA evidence found at the crime scene. Suspect 2 is not a match. Image source: Knight, Pamela. “Biosleuthing with DNA Identification.” Bio/Technology, vol. 8, no. 6, 1990. View Source

Forensic Analysis

Almost any type of biological material—skin, hair, blood, and other bodily fluids—contains a person’s DNA. Today, standard DNA analysis is accomplished by testing 20 genetic markers known as Short Tandem Repeats (or STRs) that are selected for their high degree of variability between individuals. They are also less expensive to process than longer Variable Number Tandem Repeats used originally in forensic testing.