The absence of these entities in assays containing heterokaryons sometimes leads to the formation of polykaryons. Under hypoxic conditions, one of these entities becomes unavailable for use in the maintenance of a “futile cycle,” resulting in von Hippel-Lindau syndrome. These entities can be grouped into caretaker, gatekeeper, and landscaper classes. One of these entities is the focus of a “two-hit” hypothesis posited by (*) Alfred Knudson. Another one of these entities is defective in most cases of Li-Fraumeni syndrome. A notable example of one of these genes, colloquially known as the “guardian of the genome,” (10[1])is called p53 (“P-53”). For (10[1])10 points, the inactivation or loss of what growth-regulating (-5[1])genes often result in the formation of cancerous masses (10[1])and are contrasted with oncogenes? ■END■