Answer:
The genotypes of the black seeds are BB, Bb and Bb
Step-by-step explanation:
A monohybrid cross are organisms that are heterozygous, in this case (Bb).
The monohybrid plants are both Bb.
If you do a punnet square and cross two Bb x Bb plants you will get the following genotypes:
BB, Bb, Bb and bb
Three black seed plants and 1 brown seed plant (bb)
The brown seed plants have the recessive trait b
While the black seed plant has the dominant trait.
The reason why the plants with the genotype Bb are black is because the dominant allele is B which is the black seed plant.
Therefore, any plant having the dominant allele B will physically have black seeds