SPECIALISED DNA TECHNIQUES

• Jurisdiction: Australia

SPECIALISED DNA TECHNIQUES

Laser Microdissection systems ..................................................................... [80.800]

Mitochondrial DNA analysis .......................................................................... [80.820]

Y chromosome analysis ................................................................................ [80.840]

Low copy number DNA analysis................................................................... [80.860]

Non-human DNA analysis............................................................................. [80.880]

[80.800] Laser Microdissection systems

Laser Microdissection (LMD) systems allow efficient identification and precise isolation of desired cells within cell mixtures. The ability to separate out specific cell types from a background population of many cell types, potentially from a number of sources, increases the chances of obtaining single-source DNA profiling results, thereby allowing analysts to interpret profiles with less difficulty and time. Of particular use in sexual assault cases where current methodology attempts to separate spermatozoa cells from other cells, often resulting in incomplete separation and mixed genotypes, laser microdissection enables spermatozoa cells to be selectively excised from the background mixture of biological material, thereby producing less ambiguity regarding the DNA profiling results. This technique is particularly useful for sexual assault samples that contain minute quantities of seminal material. In a dominant cellular population which overrides contributions from the minor seminal contributor, selective excision and profiling of the spermatozoa cells should greatly improve the quality of genotypes obtained, resulting in more straightforward interpretation of DNA results. Few laboratories have implemented this technology, especially since the emergence and implementation of Y profiling capabilities, which can detect male DNA without the need to isolate specific cells through the use of LMD.

[80.820] Mitochondrial DNA analysis

Within the cell and outside of the nucleus lie the mitochondria. These are subcellular units whose function is to provide the cell with energy. Within the mitochondria is a small circular DNA molecule, 16,599 base pairs in size. This DNA is termed "mitochondrial DNA" (mtDNA). The mtDNA is inherited maternally via the female ovum alone, with none of the mtDNA coming from the paternal line; maternal relationships (kinship) can thus be determined by analysing the mtDNA.

There are over 1,000 copies of the mtDNA in each cell. The abundance or high copy number of the mtDNA is useful in small or degraded samples such as hair shafts or skeletal remains. Its main application in forensic analysis is in analysing samples where nuclear DNA testing has been or is unlikely to be successful (Isenberg, 2002), although, depending on the status of the sample, results are not always obtained (Prieto et al, 2003). MtDNA, however, is time-consuming and costly largely due to the many measures required to minimise contamination (as there are over 1,000 copies per cell). To minimise the occurrence of contamination, samples are analysed one at a time with thorough cleaning procedures between samples; however, this makes the analytical process lengthy. In a number of jurisdictions in...