(c) : The given situation is an example of incomplete dominance where phenotype found in $F_1$ generation do not resemble either of the twoparents. The genotype of the two plants used forcross will be as in figure.The incomplete dominance of dominant allele (here $‘R’$) over recessive allele (here $‘r’$) could be due to mutations (insertion, deletion, substitution or inversion of nucleotides). The mutant allele generally produces a faulty or no product. This modification in the product may lead to incomplete dominance of the (unmodified) wild type dominant allele.