In sporadic cases of retinoblastoma, only two gene mutations are thought to be necessary in the same cell for a tumor to develop. This happens when an organism inherits a mutant allele and a wild-type allele forms the parents. When the wild-type allele is mutated, resulting in tumorigenesis, this process is called, .

Explanation:

When the wild-type allele is mutated, resulting in tumorigenesis, this process is called loss of heterozygosity

Tumor suppressor genes suppress the cell division (growth) and induce apoptosis

Loss in function mutation in both copies of alleles are generally recessive in nature that leads to the development of tumor because normal tumor suppressor genes are dominant in nature, protein retinoblastoma is one such example

If protein retinoblastoma is inactive then cell divides continuously but with damaged DNA cell fails to go apoptosis that leads to conversion of normal cell into cancerous cell