Final answer:
All offspring of the F1 generation from the cross of a true breeding tall plant with a true breeding short plant are expected to display the tall phenotype because the tall trait is dominant.
Step-by-step explanation:
In the F1 generation, all offspring produced from the cross between a true breeding tall plant and a true breeding short plant are expected to be tall.
The question involves an understanding of Mendelian genetics, particularly the inheritance of dominant and recessive traits. According to Mendelian principles, when two true breeding plants - one with the tall phenotype (TT) and the other with the short phenotype (tt) - are crossed, each parent contributes one allele to the F1 offspring. As the tall characteristic is dominant over the short characteristic, all the F1 offspring inherit a T allele from the tall parent and a t allele from the short parent, making them all heterozygous (Tt) but phenotypically tall because the presence of one T allele is sufficient for the tall trait to be expressed. This outcome is a result of Gregor Mendel's law of dominance, which states that in a heterozygote, one trait will conceal the presence of another trait for the same characteristic.