AP BIOLOGY

Detailed explanation-1: -The Knudson hypothesis, also known as the two-hit hypothesis, is the hypothesis that most tumor suppressor genes require both alleles to be inactivated, either through mutations or through epigenetic silencing, to cause a phenotypic change.

Detailed explanation-2: -Cancer cells silence tumor suppressor genes by Knudson’s two-hit mechanism, [1] in which a loss-of-function mutation at the tumor suppressor locus is followed by a loss of heterozygosity (LOH), and therefore a loss of the wild-type tumor suppressor gene.

Detailed explanation-3: -Tumor suppressor genes, or antioncogenes, provide negative control of cell proliferation. Loss of function of the proteins encoded by these genes, through deletion or mutational inactivation of the gene, liberates the cell from growth constraints and contributes to malignant transformation.

Detailed explanation-4: -Mutations (changes in DNA) in tumor suppressor genes may lead to cancer. Also called antioncogene.

Detailed explanation-5: -According to a “two-hit” model, dominantly inherited predisposition to cancer entails a germline mutation, while tumorigenesis requires a second, somatic, mutation. Non-hereditary cancer of the same type requires the same two hits, but both are somatic.