Laser Microdissection Separation of Pure Sprermatozoa Populations from Mixed Cell Samples for Forensic DNA Analysis

摘要

Short Tandem Repeat (STR) analysis is a valuable tool in identifying the source of biological stains, particularly from the investigation of sexual assault crimes. Difficulties in analysis arise primarily in the interpretation of mixed genotypes when cell separation of the sexual assailant's sperm from the victim's cells is incomplete. The forensic community continues to seek improvements in cell separation methods from mixtures for DNA typing. The feasibility of applying laser microdissection (LMD) technology to precisely separate sexual assault cell mixtures by visual inspection coupled with laser dissection was assessed through (a) evaluation of various histological stains for use with LMD and downstream DNA analysis, (b) identification of an appropriate DNA isolation method for LMD collected cells, (c) quantitative analysis of DNA from both sperm and epithelial cells collected by LMD, (d) Short tandem repeat typing from LMD separated sperm cells from mixtures of semen and female buccal epithelial cells using both standard and low copy number DNA analysis, and (e) a comparative study between the LMD method and the preferential lysis method for separation of sperm from epithelial cells at various mixture ratios for low copy number analysis. Also, four genuine case samples were examined using LMD.