Terms Starting with Letter: O oligonucleotide Synonym: oligo. Short, single-stranded nucleic acid. oncogene A gene whose product is involved in inducing cancer. See Proto-oncogene. optical imaging Utilizing photons in the ultraviolet to near infrared range to produce in vivo diagnostics. Including wavelengths visible to humans. organelle Any membrane limited organized structure found in or on cells. (e.g., ribosomes, nuclei, mitochondria) osteosarcoma Malignant bone tumor. outbred mice Opposite of inbred mice: distantly related mice providing the maximal variety of genetic difference.