The nonmutant allele of the brca1 gene to suppress tumor formation in women who are heterozygous for the mutation. women heterozygous for brca1 nevertheless have a 50% to 70% chance of developing breast cancer before age 70, and the usual reason is that the nonmutant allele is lost or inactivated in a lineage of cells. one possible mechanism for such "loss of heterozygosity" is:
a. germ cells in the affected individual develop a mutation in the nonmutant allele of brcal.
b. a somatic mutation in a breast cell inactivates the nonmutant brca1 allele.
c. a silent mutation occurs in the nonmutant brca1 allele.