The parents in both of the crosses look the same. Why are the results different?

 

The phenotype of an individual is directly related to the genotype of an individual and by only looking the phenotype one can not predict the genotype. Mendel have explained this by test cross. The reason i have explained in the next section

Step-by-step explanation

According to Mendel principles the phenotype of an individual directly related to its genotype.

Case 1- If there is a cross between homozygous tall pea plant ( TT ) and hetrozyzous tall pea plant ( Tt ) then result would be as follows-

TT * Tt

TT Tt TT Tt

Here in this cross the phenotype of both the parent is same means both are tall because in homozygous tall plant both the alleles are dominant and in heterozygous tall plant one allele is dominant that is T and other allele is recessive that is t ( non expressive ). Result of the cross would be - all the offsprings will be tall phenotypically but genotypically different means two are homozygous tall plant ( TT, TT ) and two are heterozygous tall plant ( Tt, Tt ).

Case 2 - If there is a cross between two heterozygous tall plant ( Tt, Tt ) then result would be as follows-

Tt * Tt

TT Tt Tt tt

Here in this case also the phenotype of both the parent is same ( both are tall ) because both are heterozygous dominant ( Tt ). When there is a cross between two the result would be different from case 1 - three offsprings are tall in which one is homozygous tall ( TT ) and two are heterozygous tall ( Tt, Tt ) and one offspring is homozygous dwarf ( tt ).

So in both the case parents look same means but the result of cross were different