Explanation

Option B is correct because a 2:1 ratio in a monohybrid cross from two heterozygotes suggests lethality in the homozygous dominant genotype. Option A is incorrect because lethal genes are specified as being in homozygous individuals, not heterozygous ones. Option C is incorrect because epistasis describes gene interaction affecting pigment or color, not necessarily causing a specific 2:1 ratio due to lethality. Option D is incorrect because option B provides a known genetic mechanism that explains the observed ratio.