Final answer:
The Hfr conjugation experiment demonstrated that genes are involved in the integration of foreign DNA into the bacterial chromosome.
Step-by-step explanation:
The experimental observation that demonstrated genes are involved in the integration of foreign DNA into the bacterial chromosome was the Hfr conjugation experiment. In this experiment, different Hfr strains of bacteria, each with an F plasmid inserted into different sites on the bacterial DNA, were mated with F- bacteria with mutations in known bacterial genes.
By analyzing the order of the genes in their offspring, it was found that the foreign DNA from the Hfr strain had integrated into the recipient bacterial chromosome. This experiment provided evidence for the involvement of genes in the integration of foreign DNA into the bacterial chromosome.