The location of a deletion that removes the last exon of the DKC1 gene. The upper line shows the last exons of DKC1and MPP1 genes on the normal chromosome, with the direction of transcription indicated by the long arrows. The vertical bars show the position of the breakpoints of the deletion that gives rise to the deleted chromosome in patient HO, shown on the lower line. The DNA sequence at these breakpoints is shown. Solid boxes indicate coding sequences; shaded boxes indicate 3′UTR sequences. The location, direction, and names of the oligonucleotides used in various PCR experiments are shown as arrowheads.