When Mendel crossed a pure tall plant with a pure dwarf plant, he found that all offsprings were tall like one of the parents in F1 generation. This meant that only one of the parental traits was seen, not a mixture of the two. Next he tried to find whether the tall plants in F1 generation were the same as the tall plants of the parent generation.
For this, he allowed the hybrid talls of F1 generation to self fertilize. However the F2 generation plants were not all tall. They showed both tall and dwarf offsprings, but the tall plants were in much greater number than the short plants. In F2 generation, their ratio was 3:1 (tall : short). This indicated that both tallness and shortness traits were inherited in the F1 plants, but only the tallness trait was expressed.
Hence he concluded that tallness is dominant over dwarfness. The character which manifested in F1 generation was called dominant and the other which was suppressed was called recessive.
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