In the familial form of retinoblastoma, individuals who inherit one mutant allele of the RB1 gene have an 85% chance of developing retinoblastoma and other cancers. Explain why, when these individuals carry only one copy of the mutant gene, there is such a high incidence of cancer in these RB1 heterozygotes
What will be an ideal response?
Those who inherit the mutant allele carry it in all of their somatic cells, and loss of heterozygosity by mutation of the normal allele anywhere in the body can result in cancer. Since there are approximately 1013 cells in the body, chances are very high that a mutation will occur in at least one cell in the normal allele at some point during an individual's life and lead to cancer.
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