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Old 02-15-2015
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Default NBME 13 question - Loss of heterozygosity

A 54 yr old man has a squamous call carcinoma of the right lung. Analysis of his germ line DNA shows two alleles, m and n, at the micro satellite locus Z, tightly linked to the p53 gene. Similar analysis of the neoplastic cells shows the presence of the m allele only. These findings are due to which of the following processes?
A. GERMLINE MOSAICISM
B. LOSS OF HETEROZYGOSITY
C. P53 GENE AMPLIFICATION
D. PERICENTRIC INVERSION INVOLVING P53 AND LOCUS Z
E. POINT MUTATION OF ALLELE n

I know the answer is B but why did the patient get Ca if he still has one normal allele???
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Old 02-15-2015
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Originally Posted by spinal View Post
A 54 yr old man has a squamous call carcinoma of the right lung. Analysis of his germ line DNA shows two alleles, m and n, at the micro satellite locus Z, tightly linked to the p53 gene. Similar analysis of the neoplastic cells shows the presence of the m allele only. These findings are due to which of the following processes?
A. GERMLINE MOSAICISM
B. LOSS OF HETEROZYGOSITY
C. P53 GENE AMPLIFICATION
D. PERICENTRIC INVERSION INVOLVING P53 AND LOCUS Z
E. POINT MUTATION OF ALLELE n

I know the answer is B but why did the patient get Ca if he still has one normal allele???
His GERMLINE has the heterozygote genotype. Loss of heterozygosity (being MM) in somatic cells has led to the cancer.
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