A quick scan of the 11 Stainless Steel Rat books shows no use of the term "DNA".
Genetics are, however extensively discussed in the novels with references to natural genetic traits, accidental mutation and forced genetic manipulation.
There are few malcontents and even fewer that are socially
maladjusted. The few of these that are born, in spite of centuries of
genetic control, are caught early and the aberration quickly adjusted. - The Stainless Steel Rat
"Yum," I said, chewing on a fragrant morsel. "My thanks to the genetic
engineers who dreamed this one up. Gourmet food-and growing on trees.
If it weren't for the inhabitants this planet would be a paradise." -
Stainless Steel Rat Sings the Blues