INTRODUCTION

• Jurisdiction: Australia

Introduction ................................................................................................... [80.100]

The basis of DNA variation ........................................................................... [80.120]

Sources of DNA ............................................................................................ [80.140]

[80.100] Introduction

Deoxyribonucleic acid (DNA) evidence is frequently presented in courts. Where previously large amounts of biological material from fluids such as blood were required (a stain approximately the size of a 20 cent coin), profiles are now routinely obtained from minute quantities of biological fluid and from samples where biological material other than fluid is present.

The impact of these advances, not only on the justice system but also in all areas of biological science, has dramatically increased the range of legal cases where DNA evidence is available. While DNA evidence was once available only in cases involving the transfer of biological fluid (eg, homicide, sexual assault), it is now routinely used in cases where no visible fluid is present (eg, armed robbery where, eg, DNA could be recovered from the inside of a head cap left behind at a crime scene).

This chapter is an overview of DNA profiling in Australia, presented in a manner intended for non-scientists, such as lawyers, to follow. Although the focus is on the Australian approach, the content is relevant wherever DNA has evidential application. For further, more in-depth information, readers should refer to Butler (2010), Goodwin et al (2010) or any good basic textbook on biology or genetics. Unless otherwise noted in this chapter, reference to DNA is to nuclear DNA.

[80.120] The basis of DNA variation

The human body is made up of different types of tissue, such as muscle tissue, bone, blood and skin. These different types of tissue are made up of a collection of cells, these being the building blocks of human, animal and plant bodies. The cell is made up of a nucleus (that contains DNA), surrounded by a liquid material called the cytoplasm, which is, in turn, encased in the cell membrane: see Figure 1, which illustrates the basic structure of a cell. The cytoplasm contains various structures such as the mitochondria (which also contain DNA), which supply the cell with energy to function. Mitochondrial DNA is discussed at [80.820]. Not all cells contain all sub-cellular components such as the nucleus and mitochondria. For example, red blood cells do not contain a nucleus or mitochondria and therefore do not contain nuclear or mitochondrial DNA. DNA extracted from blood is sourced from the white blood cells. Tissue and cells deposited on a...