A genomic blueprint for bison recovery was also blurred by private herd managers who experimented with cattle crossbreeding during the 20th century. While these efforts were generally unsuccessful, they introduced a persistent belief that most bison today possess cattle ancestry because of these attempts.
By using ancient, pre-cattle bison as a clean genetic baseline—a first for this kind of study—the research team found cattle ancestry in only about a third of modern bison. And when present, Shapiro said, it was a small fraction of the genome—under 2%—and traceable to a limited window of hybridization roughly 20 generations ago.
Paleogenomic insight into the collapse, recovery, and management of American bison
Decoding the North American bison’s genome
I posted before that every bison had some cattle genes. That has been refined.