June 24, 2020
DNA, Sexual Offences
Microscopic preparation from a vaginal swab stained with semen (400x magnification)
The Crown’s forensic report states that semen has been detected and that a DNA profile matching your client has been found.
You might assume that the DNA came from the semen.
But that may not always be correct!
The reason is that the DNA could originate from another body fluid or cells present in the same area as the semen and therefore any attribution of the DNA profile to the semen present may not be robust.
Semen consists of a fluid (seminal fluid) which contains spermatozoa (sperm cells). Although the DNA profiling process usually includes a step that preferentially extracts DNA from the sperm rather than from any other cells, this is not always 100% effective. In other cases, because the amounts of semen are so low, this preferential extraction step is not used.