(A) Ethidium bromide–stained agarose gel showing PCR products for minisatellite CEB285. Six different alleles are scored among 32 individuals (in some cases, three bands are seen for one individual [the upper one is a PCR artifact as shown by segregation patterns in families]; this artifact occurs only in heterozygotes [data not shown], indicating a mechanism involving an interaction between the two alleles). (B) Image of the gels obtained for minisatellites CEB205 and CEB310 on CEPH families 884 and 1331, respectively. Two children inherit mutant alleles for CEB205, and one child inherits a mutant allele for CEB310. For CEB205, larger alleles are missed in the procedure used: The results were confirmed by Southern blot.