Uncertain Sex Every now and then, a baby is born with “ambiguous genitals,” meaning that the child’s sex is not abundantly clear. When this happens, a quick analysis of the chromosomes is needed, to make sure there are exactly 46 and to see whether the 23rd pair is XY or XX. The karyotypes shown here indicate a typical baby boy (left) and girl (right).

BIOPHOTO ASSOCIATES/SCIENCE SOURCE