CLONING, CHARACTERIZATION AND CHROMOSOMAL LOCATION OF A SATELLITE DNAFROM THE PACIFIC OYSTER, CRASSOSTREA-GIGAS

We report the cloning and characterization of a high-copy-number, tand em-repeat satellite DNA sequence from the genome of the Pacific oyster , Crassostrea gigas (Cg). The monomeric unit was found to be 166 (+/- 2) bp in length with 79-94% homology between monomers of the array. Th e sequence is Af T-rich (60%) and lacks internal repetition and substr uctural features. The repeat was estimated to account for 1-4% of the Cg genome. Fluorescence in situ hybridization (FISH) studies mapped th e repeat to two distinct heterochromatic regions of two pairs of homol ogous chromosomes on Cg embryonic metaphases. Also, the number of meta phase chromosomes containing this repeat varied with the ploidy of the cell.