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There are two types of pea plants according to Mendel: 1)Tall(TT or Tt) 2)Dwarf(tt) But I have a doubt! Is there a heterogeneous dwarf pea plant(tT)? When there can exist a heterogeneous tall pea plant, there must exist a heterogeneous dwarf pea plant also! This doubt is troubling me very much! Please clear my doubt!

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Why there must exist a heterogeneous dwarf pea plant also. I don't understand why you think it must be the case.

Under this simple genetic model, there is no environmental variance and T is dominant over t (t is therefore recessive) and therefore the heterozygotes Tt have the same phenotype than the homozygote TT. There is no Tt individuals that have the same phenotype as tt.

If t was dominant, then Tt individuals would have the same phenotype as tt individuals. If T and t were perfectly additive, then Tt individuals would have a phenotype half way between the TT and the tt phenotypes (Tt would be of average height).

Please note, that very few real life cases are that easy. There is often interaction between many loci and there is often (if not always) environmental influence on the phenotype.

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