Individuals Heterozygous for the RB⁺ and RB⁻ Alleles Can Develop

Individuals heterozygous for the RB⁺ and RB⁻ alleles can develop tumors as a result of (Select all that apply. )

A) a mitotic crossover that leads to homozygosity for RB⁺ in some cells and RB⁻ in other cells.
B) a somatic mutation in the RB⁺ allele that leads to homozygosity for RB⁻.
C) a somatic mutation in the RB⁻ allele that leads to homozygosity for RB⁺.
D) the fact that RB⁻ is dominant to RB⁺.