Genotyping results for the patient and his parents. (A) DNA sequencing for the c.20A>T (Hb S) mutation of propositus and parents. The propositus' 8% mosaicism for the wild-type allele (Hb A) was below the detection limit of the assay, and he appeared homozygous Hb SS. The mutation is marked by the red arrowhead. (B) Results of genotyping with chromosome 11 polymorphic STR markers to define the patient's UPD. The region of mosaic UPD is marked by the red bar next to the chromosome 11 ideogram. The dashed portion of the bar represents uncertainty in which the UPD begins. The locations of the HBB gene (11p15.4) and the BWS locus (11p15.5) are marked. The panels at right show electropherograms of 2 STR markers amplified by PCR from leukocyte DNA of the patient and his parents. Large left-facing arrows mark the positions of the markers on chromosome 11. For each marker, small black arrows point to the allele transmitted from the father to the patient, and small red arrows point to the allele transmitted from the mother. D11S898, an STR outside the region of UPD (11q22.1), shows normal biparental inheritance. At D11S1338, within the region of mosaic UPD (11p15.4), the patient has a significantly reduced maternal allele.