Cytogenetics of Oysters

Abstract

The paper reports a comparative chromosomes study of six species of Crasso-strea and three of Ostrea. Of these, six species occur in Karachi, West Pakistan and three on the Pacific coast of the U.S.A. Chromosomes of 18 males and 92 females were examined from germ-line cells and early embryonic mitoses.Meiosis was found to be chiasmate and photographs of first metaphase biva-lents of spermatocytes are being published for the first time. A 2n=20 (n=10) is common to all oysters. Karyotypes contain only metacentric (M) and sub-metacentric (S) chromosomes and are symmetrical and outwardly identical. Fluctuations were observed, however, in the frequencies of M and S elements in different species and have been attributed to pericentric inversions or centric shifts.