Table 3.
Comparison of partial matching, familial searching, IGG and Y-STR searching indirect matching.
| Technique | Partial Matching | Familial Searching | Investigative Genetic Genealogy | Y-STR searching and other indirect matching techniques coupled with kinship analysis |
|---|---|---|---|---|
| How method is initiated | Random or semi-randomly occurring | Targeted search | Targeted search | All forensic profiles proposed |
| DNA type used | STRs | STRs, frequently followed up with Y-STR comparison to limit adventitious matches | SNPs after STRs do not directly match | Y-STR or other search key, followed by STR comparison and kinship analysis, followed by IGG depending on kinship analysis outcome |
| Database used | No database search necessarily occurs | CODIS | Consumer Genealogy Databases | Forensic profiles are be compared directly to each other enabled by a basic spreadsheet program or more advanced database tools |
| Comparison | Samples are compared one against another and evaluated with kinship analysis | A kinship algorithm calculates a likelihood ratio (LR) statistic for every profile in the database against the forensic profile and results are sorted from highest LR to the lowest | All profiles in the database are compared against the forensic profile for areas of shared DNA, measured in centimorgans (cM). Indirect matches are provided in order of highest matching cM value. | Y-STR or other search keys are compared among forensic profiles looking for matching profiles. For profiles with the same key, then the autosomal STR profile is evaluated using kinship analysis. Immediate family members are reported. More distant relatives are considered for IGG |
| Estimated chances of success | Varies widely based on similarity of profiles to each other; can be scrutinized by kinship analysis | 20–25% [48] | 60% or more depending on size of database and amount of genealogical research conducted [52] | 20% or more initial success on all cases based on Business Case provided using identical twin extrapolation, then IGG success on remaining targeted major cases |
| Usage | Randomly occurring in casework, with some laboratories having established policy if profiles that appear to be similar are found | 12 American states and numerous countries, UK, Australia; prohibited in Maryland and District of Columbia (U.S), Germany, and some EU countries [48] | Utilized in over 33 U S. States, Canada, Sweden, enabled by Maryland State legislation with judicial oversight and approval; prohibited in Germany [14] | Novel application of existing methods of comparison of profile keys, coupled with kinship analysis. Each component of the technique is separately utilized in many forensic laboratories |