The phrase "genetic traces" refers to small pieces of genetic information or DNA that can be used to identify or trace back an individual or their ancestors. Full definition
The Mexican scientists looked for genetic traces of the cabbage mosaic virus, which is used to carry modified DNA sequences into plants. (sciencemediacentre.org)
It seems that our ancestors met, leaving a small genetic trace of these ancient relatives in our DNA. (religion.blogs.cnn.com)
And indeed, Borucki found genetic traces of the outbreak virus even in the earliest samples. (scientificamerican.com)