What would be a typical phenotypic monohybrid ratio in which a lethal allele is involved?13:52:19:3:3:13:1 (it is not this one)6:2:3:1 Solution Answer- 2:1 Explanation- The normal genotypic ratio upon crossing two heterozygotes is 1(homozygous dominant) :2 (heterozygous):1(homozygous recessive). A 2:1 phenotypic ratio indicates that the homozygous recessive individuals show lethal gene effect and are not born..