Yields frequent detachments resulting from exchange between the Y chromosome and the interstitial heterochromatin of the reversed acrocentric and preferential recovery of the proximal X. Tetrad distribution usually quite abnormal; one-exchange tetrads infrequent and no- and two-exchange tetrads frequent. Exchange frequency increased by addition of Y or y⁺YL, but tetrad distribution remains abnormal (Sandler, 1954). YL appended as a second arm to C(1)RA normalizes tetrad distribution (Sandler, 1958). Tetrad distribution is normal in more recently recovered C(1)RA chromosomes (Sandler and O'Tousa, 1979), reason for differences between 1954 and 1979 data is unclear. The presence of a Y chromosome or a free-X duplication as a homologue markedly increases both exchange between the elements of the compound and fecundity of compound-bearing females.

Novitski.

between the proximal heterochromatin of X.YL and the distal heterochromatin of In(1)sc⁸ or possibly by sister-strand union in one of the heterochromatic segments followed by a normal euchromatic exchange. A frequently recurring event that seems to require the presence of YL. More recent attempts to repeat such constructions have been unsuccessful, except in response to X-irradiation.