Which of the following statements is the most likely explanation for a particula

Question

Which of the following statements is the most likely explanation for a particular cancer appearing in several members of the same family?

a. Affected individuals have inherited a defective allele whose product interferes with DNA synthesis.

b. Affected individuals have inherited a defective allele whose product interferes with with mismatch repair.

c. Affected individuals have inherited a defective allele whose product interferes with the synthesis of purine nucleotides.

d. Affected individuals have inherited a cancer-causing gene that was mutated in the ancestor’s somatic cells.

Please provide a brief explanation as to why

Explanation / Answer

Ans: The most likely explanation, for a particular cancer appearance in several members of the same family, is (b) i.e Affected individuals have inherited a defective allele whose product interferes with the mismatch repair. Because, Cancer is not caused by a single gene defect. Accumulation of various mutations, that lead to dismantle the balance or regulation of cell growth and proliferation, causes cancer.

(a) If affected individuals have inherited a defective allele whose product interferes with DNA synthesis then there are check-points in the cell to ensure the DNA replicates only once to allow the cell to complete the cell cycle. Hence any disregulation in DNA synthesis will hamper the cell proliferation and no cancer will develop.

(b) If affected individuals have inherited a defective allele whose product interferes with mismatch repair then there are chances that mismatches during DNA synthesis may lead to mutations in genes such as oncogenes and tumor suppressor genes which will result in cancer. Oncogenes in normal condition regulate the cell growth and tumor suppressor genes in normal condition maintain the cell cycle check-points.

(c) If affected individuals have inherited a defective allele whose product interferes with the synthesis of purine nucleotides then it will lead to purine nucleotides scarcity which will hamper the DNA synthesis and no cell proliferation will take place to form a cancer.

(d) Affected individuals have inherited a cancer-causing gene that was mutated in the aancestor's somatic cell- This option is ruled out because any mutation in somatic cells can not be passed on in generations and hence can not be a cause of hereditary mutation leading to cancer.

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