| In the field of forensic science, animal biological evidence is playing an increasingly important role. Dogs (Canis lupus familiaris) are kept as pets in 39% of American households, thereby being a domesticated species of significant forensic interest. Since animals can be the victim, perpetrator, or witness of a crime, animal biological evidence at a crime scene may be forensically important. As with any biological evidence, the condition of that evidence is always of utmost importance. Sample degradation can occur from exposure to various factors including bacteria, heat, ultraviolet light (UV) and soil. Obtaining a complete nuclear STR profile is difficult with degraded DNA. To help solve the problem of generating complete nuclear profiles from degraded samples, scientists in the human forensic DNA field have developed mini short tandem repeat (STR) primer sets, which amplify shorter segments of DNA than the commonly used STR primer sets. This same technique for degraded DNA analysis can be applied to canine STR panels. Currently the UC Davis Veterinary Genetics Laboratory uses a validated sixteen loci multiplex STR panel, the VGL Canine Panel, for use with canine forensic samples. This STR panel was redesigned to produce smaller amplicons that are under 205 bp, and separated into three panels of STRs instead of one multiplex. Also, in an effort to increase sensitivity, a smaller reaction volume was explored, allowing a smaller amount of input DNA. These new miniSTR panels were validated using degraded, inhibited, and casework-type samples and the results compared with results from the VGL Canine Panel to demonstrate the significant improvement the miniSTRs provide. The data obtained from the validation indicates the new VGL Canine MiniSTRs will increase the likelihood of obtaining complete or near complete profiles from poor-quality samples that have failed to produce complete profiles using the larger sixteen multiplex STR panel. For the VGL Canine Panel, optimum input DNA is 0.5--1.5 ng with full DNA profiles obtained with160 pg. The VGL Canine MiniSTRs using the small volume reaction were shown to produce full profiles with 63 pg DNA, resulting in a three-fold increase in the sensitivity. |
