History of forensic DNA profiling in criminal investigations

Advertisement

Discovery of structure and importance of DNA molecule:  A Nobel prize Mendelian law of inheritance

The history of DNA can be thought of as beginning with an Austrian (now Czech Republic) Augustinian monk, Gregor Mendel, who is called the founder of genetics. In 1865, he completed a series of experiments with peas and showed that certain traits, such as shape and color, were inherited
in different packages—now called genes. When crossing white flower and purple flower plants, Mendel found that the result was a purple flower, not a blend of the colors. He conceived the idea of heredity units  that were either recessive or dominant (Mendel, 1865). These units (genes)
normally occur in pairs in body cells but segregate during the formation of sex cells. A dominant gene will hide a recessive gene. Mendel stated that each person inherits two traits from each parent. If
the traits are the same, they are homozygous; if they are different, they are heterozygous. This becomes an important factor for forensic scientists and lawyers when interpreting DNA profiles. The alternative forms of each trait are called alleles.

The two principles Mendel described were the Law of Segregation, by which each parent passes a randomly selected allele to its offspring during fertilization, and the Law of Independent Assortment, by which separate genes for separate traits are passed independently from parent to child. Of the 46 chromosomes in a human cell, half are from the mother’s egg and the other half from the father’s sperm.
 
Structure of DNA
Until a scientific paper was published in 1944 (Avery et al.), biologists thought that genes—the units of inheritance—were made of proteins. Oswald Avery, an American scientist, managed to transfer the ability to cause disease from one strain of bacteria to another, showing the connection between nucleic acids and genes. This paper has been described by Nature, a leading scientific journal, as the defining moment in nucleic acid research.

The following decade saw the amazing discoveries of the structure of DNA and how it is copied from one generation to the next. Linus Pauling in California postulated a triple helical structure for DNA in 1953. So had James Watson and Francis Crick working at Cambridge in England, but they were all wrong. It was Rosalind Franklin’s x-ray diffraction photograph that was (unbenownst to her) shown to James Watson that revealed the true structure of DNA to Watson and Crick.

Nature considers the year 1953 an annus mirabilis (year of wonders) for science. The three-
dimensional structure of DNA was first described by Watson and Crick in April 1953 in a Nature article. This was the first explanation of how genetic information is encoded and transferred from one
generation to the next. This classic paper first describes the double helical structure of DNA. Nature later stated that the authors noted “with some understatement that the structure suggests a possible copying mechanism for the genetic material.” Another paper in the same issue of Nature
analyzes the x- ray crystallography evidence and suggests that a double helical structure exists in biological systems

Following on from this, Rosalind Franklin and Ray Gosling, her student, provided further evidence of the helical natures of nucleic acids and concluded that their phosphate backbones lie on the outsides of the structures (Franklin and Gosling, 1953). In the next month’s issue of Nature, Watson and Crick followed up with largely accurate speculation on how the base pairing in the double helix allows replication of DNA (Watson and Crick, 1953).

Advertisement