Final answer:
The genotypes TT (homozygous dominant) and Tt (heterozygous) in pea plants result in the same phenotype: a tall pea plant. This is because in both cases, the dominant allele for tallness (T) is present, which masks the presence of the recessive allele (t) in the heterozygous genotype.
Step-by-step explanation:
The plant height genotypes TT and Tt in pea plants are similar because they both result in the same phenotype: a tall pea plant. The TT genotype represents a pea plant that is homozygous dominant for the tall trait, meaning it possesses two dominant alleles, and thus, displays the characteristic associated with the dominant allele, which is tallness. On the other hand, the Tt genotype is heterozygous, containing one dominant allele (T) and one recessive allele (t). Here, the tallness trait still prevails because the presence of the dominant T allele is sufficient to mask the effect of the recessive t allele, as per Mendelian genetics.
When crossing TT and tt plants, all of the F1 generation will be heterozygous Tt and will exhibit the tall phenotype. Upon self-pollination of the F1 generation, the potential genotypic combinations in the F2 generation are TT, Tt, tT, or tt, with a phenotypic ratio of tall to dwarf plants being 3:1 given that 75% would have at least one dominant T allele reflecting tallness.