Chromosome 21 is the smallest human autosome.

The gene is disrupted in six patients with X;autosome translocations or submicroscopic deletions; nine patients had point mutations.

This is the first report of a live born girl with an X-autosome translocation involving the ZIC3 region.

Methods: We report mapping of novel breakpoints of X;autosome-balanced translocations and interstitial deletions and a review of published X chromosome rearrangements.

The human Y chromosome, transmitted clonally through males, contains far fewer genes than the sexually recombining autosome from which it evolved.