Gene retention is a related term in genetic testing, in which specific genes or their fragments are detected in cells by techniques such as PCR to study whether the gene or fragment is lost during the developmental stage of the cell. Detecting gene retention is a scientific research tool that is involved in genetic engineering as well as in tumor biology diagnosis. In genetic engineering, it is generally believed that if the exogenous gene is not integrated during embryonic development, it will be slowly lost, and the retention rate will gradually decrease, and the later the development, the closer the retention rate is to the integration rate, which is a theoretical guidance for the study of gene integration and for the practice of improving varieties by transgenic technology. For tumors and certain diseases, the retention rate of specific genes or their fragments in tissues can reflect the lesions to a certain extent, and the study of gene retention rate may become a new biological diagnostic method for diseases.