We will take case of monohybrid inheritance.
(i) Mendel crossed the tall plants with the dwarf plants and found that only the tall pea plants were produced in the first generation (F1). No dwarf plants were obtained in that generation. He concluded that the first generation showed the traits of only one of the parent plants that is tallness here. The traits of other parent does not show here.
(ii) He then crossed the tall plants of the first generation and found that tall plants and dwarf plants were obtained in the second generation in the ratio of 3:1. In other words in F2 generation, three fourth plants were tall and one fourth was dwarf.
(iii) Thus he concluded that the dwarfness was not lost but was merely suppressed in first generation that appeared again in the second generation. He called this repressed trait as ‘recessive trait’ and expressed the tallness trait as the ‘dominant trait’ .
(iv) Also it was observed that the traits in the first generation were either tall or dwarf but were not intermediate. In this way it was specified that the traits are inherited independently. The ratio 3:1 is known as the monohybrid ratio.
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