SRY on the Y chromosome initiates male sex determination. We tested a
phenotypic female with sex chromosome mosaicism, X/XYY, for SRY expres
sion. SRY was determined by polymerase chain reaction (PCR) amplificat
ion in genomic DNA from a female patient with a sex chromosome mosaic
complement, 45,X/47,XYY, followed by sequencing analyses. The patient
yielded the PCR product with predicted size and homology to the consen
sus sequence of SRY. The demonstration of SRY provides evidence that t
he female phenotype in the presence of sex chromosome mosaicism, X/XYY
, may result from alterations in another part of the sex-determining p
athway or downstream from SRY.