A pea plant with genotype Bb is crossed with a plant with genotype bb. What do the four boxes contain?

الشرح

One parent puts b into every gamete, so no box can receive two dominant alleles, while the other parent sends B half the time and b half the time. That leaves two boxes with a mixed pair and two with a recessive pair, which is why a genotype of two dominant alleles cannot appear in this cross.