Monohybrid Ratio:Mendel carried his experiment by crossing varieties of garden peas and recording his results. In pea he found a number of contrasting characters, e.g., tall or dwarf plants; purple or white flowers; and yellow or green, wrinkled or smooth seeds. In one series of experiments he selected darkness and tallness of plants. Pure breed of tall plants were found out by breeding tall plant with tall for several generations which had produced tall plants only. Similarly, dwarf plants were also collected.
The experiment was started by breeding tall plants with dwarf plants. This generation is known as the parental generation. When tall plants of pure strains were crossed with dwarf plants of pure strains it was found that all the plants were tall. This generation is called the first filial or F generation or hybrid generation.
Thus all the plants of the F, generation resembled only one parent, the tall one. Next, the members of the generation were crossed with each other and different results obtained. The second or the F2generation gave rise to a mixed generation of tall and dwarfed no intermediate) in the ratio of 3: 1. When the dwarf plants were crossed with one another, it was found that all the plants w dwarf. And this was true for every dwarf tested. But with the tall it was not so.
Though then plants were indistinguishable in appearance, some of them bred true to type, that is, they gave rise to tall plants only, while others behaved like the original tall hybrid, splitting up in to tall and dm in the ratio of 3 : 1. If we denote a true breeding tall plant as T, a dwarf plant as D, and a tall which gives both tall and dwarf plants in the ratio of 3: 1 as T (D).