CHARACTERIZATION AND IDENTIFICATION OF OYSTER CHROMOSOMES BY FISH

¹ Haskin Shellfish Research Laboratory, Institute of Marine and Coastal Sciences, Rutgers University, 6959 Miller Avenue, Port Norris, NJ 08349 USA

² Department of Biological Sciences, University of Science in Philadelphia, 600 South 43rd Street, Philadelphia, PA 19104 USA

Characterization and identification of chromosomes are needed for several types of genomic analyses and mapping. Although oysters have a low haploid number of 10, oyster chromosomes are difficult to characterize because of their similarities in size and shape. Traditional banding techniques in oysters have been difficult and unreliable. Fluorescence in situ hybridization (FISH), on the other hand, may provide a powerful tool for the identification and physical mapping of oyster chromosomes. We tested FISH on oyster chromosomes with several types of DNA sequences and probes using chromosomes from early embryos. The vertebrate telomere probe, (T2AG3)n, produced strong hybridization signals at ends of all oyster chromosomes, suggesting that this sequence is also present in telomeres of oysters. No interstitial sites were detected for the telomere sequence. A rDNA probe was produced by PCR-labeling and assigned to the second largest chromosome (Chromosome 2) in the American oyster. Interestingly, the same rDNA sequence was located on the smallest chromosome (Chromosome 10) in the Pacific oyster. Anonymous repetitive DNA fragments produce strong signals on multiple chromosomes. Unique sequences from P1 clones are also being tested for chromosome assignment.