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Question
Two independent monohybrid crosses were carried out involving a tall pea plant with a dwarf pea plant. In the first cross, the offspring population has equal number of tall and dwarf plants, whereas in the second cross it was different. Work out the crosses and explain giving reasons for the difference in the offspring population.
Solution
A monohybrid cross is a cross where two forms of a single trait are hybridised. Mendel crossed pure tall pea plant with a pure dwarf pea plant and obtained all tall plants in the first filial generation. The character which appeared in the F1 generation is called dominant character, whereas the character which is not expressed in the F1 generation is called recessive. After inter-crossing the hybrids of the F1 generation, he obtained tall and dwarf progeny in the ratio 3:1 (phenotypic ratio), but the genetic ratio was 1:2:1 which is TT, Tt and tt.
Such a cross depicts the law of dominance in which all traits are controlled by a pair of factors called genes. In a dissimilar pair of factors, one member of the pair is dominant, while the other is recessive.
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