Because we know that 15% of the population does not have the allele we can assume that at least 85% of the population has at least on copy of the dominant allele.
Basically Hershey and Chase studied bacteriophages (viruses that infect and destroy bacteria), which they got the idea from Avery who got the idea from Griffith.
so the results of Hershey and Chase's experiments were that genes are made from Deoxyribonucleic Acid.
hopefully this helps