Final answer:
Plants with genotypes BB (homozygous dominant) and Bb (heterozygous) both produce a purple-flower phenotype due to the dominance of allele B. In incomplete dominance, RW heterozygous plants show pink flowers. Similarly, in pea plants, both YY and Yy genotypes have a yellow seed phenotype, though their genotypes are different.
Step-by-step explanation:
An example of two plants with different genotypes but the same phenotype could be in the context of flower color inheritance. For instance, if a plant species has two alleles for flower color, where purple is dominant (B) and white is recessive (b), then a plant with a genotype of BB (homozygous dominant) or Bb (heterozygous) would both exhibit the phenotype of purple flowers. This is because the dominant B allele masks the expression of the recessive b allele when they are together in a heterozygote.
In contrast, an example of incomplete dominance could be a plant with a red allele (R) and a white allele (W) where the alleles show incomplete dominance. Here, a plant that is homozygous for the red allele (RR) will have red flowers, while a plant with a heterozygous genotype RW will have pink flowers, which is a blend of red and white phenotypes. Neither allele is completely dominant in this case.
To further clarify, Mendel's experiments with pea plants showed that the phenotype can hide the underlying genotype. For example, in pea plants, the yellow-seed allele is dominant (Y) and the green-seed allele is recessive (y). A plant with a genotype of YY (homozygous dominant) or Yy (heterozygous) would both show a phenotype of yellow seeds despite their different genotypes.