  We investigate the consequences of adopting the criteria used by the state of
California, as described by Myers et al. (2011), for conducting familial
searches. We carried out a simulation study of randomly generated profiles of
related and unrelated individuals with 13-locus CODIS genotypes and YFiler
Y-chromosome haplotypes, on which the Myers protocol for relative
identification was carried out. For Y-chromosome sharing first degree
relatives, the Myers protocol has a high probability (80 - 99%) of identifying
their relationship. For unrelated individuals, there is a low probability that
an unrelated person in the database will be identified as a first-degree
relative. For more distant Y-haplotype sharing relatives (half-siblings, first
cousins, half-first cousins or second cousins) there is a substantial
probability that the more distant relative will be incorrectly identified as a
first-degree relative. For example, there is a 3 - 18% probability that a first
cousin will be identified as a full sibling, with the probability depending on
the population background. Although the California familial search policy is
likely to identify a first degree relative if his profile is in the database,
and it poses little risk of falsely identifying an unrelated individual in a
database as a first-degree relative, there is a substantial risk of falsely
identifying a more distant Y-haplotype sharing relative in the database as a
first-degree relative, with the consequence that their immediate family may
become the target for further investigation. This risk falls disproportionately
on those ethnic groups that are currently overrepresented in state and federal
databases.
