A mutation in a gene involved in fruit colour in tomato plants, ${Solanum\ lycopersicum}$, leads to yellow fruits being produced instead of red fruits. A genetic cross was carried out between a pure breeding plant with a red fruit and a pure breeding plant with a yellow fruit to produce the F1 generation. All offspring plants produced red fruits. The F1 plants were then crossed with each other and the seeds produced were planted to obtain the F2 generation. Construct a genetic diagram to show the cross of the F1 generation that produced this F2 generation. Use the symbols $R$ and $r$ for the alleles.
A hypothetical dihybrid cross contains two genes situated on different autosomes. Each gene has two alleles, with one dominant and one recessive. A parent that is homozygous dominant for both genes is crossed with a parent that is homozygous recessive for both genes. This yields F1 individuals, which are then crossed to produce the F2 generation. State the phenotypic ratio of this dihybrid F2 generation and explain why some of these offspring phenotypes differ from the original parental phenotypes.