In monohybrid cross of red and white flower, Mendel got only red flower. On setting the F, plants having red flower he got both plants with red and white flower. Explain the basis of using RR and rr symbols to represent the genotype of plants of parental generation.

Explanation

On crossing red and white flower only red colour flower appeared in the `F_1` generation. But the white colour flower again appears in the `F_1` generation which is raised out of the `F_1` individuals only. Mendel reasoned that there is a factor of each and every character. Accordingly, there has to be one factor(R) for red flower and other one factor (r) for white flower. In case, an organism possess only one copy of the gene then the possibility of reappearance of white flower in the `F_2` generation of the given cross is not there. Also the ratio (3:1 of red and white) indicates that each organism must possess two copies of a particular gene.