Gene for plant height has two alleles: T and t. Here, "T" is the allele for tallness and "t" allele imparts dwarf phenotype of the plants. True breeding plants are the one that have two copies of either "T" or "t" True breeding tall plants have genotype "TT" and true breeding short plants have genotype "tt". There, cross "TT x tt" denotes Mendel’s cross of true-breeding tall plants with true-breeding short plants in a Punnett square
