Final answer:
A pea plant with a genotype of Tt is referred to as heterozygous, expressing a tall phenotype because the dominant allele 'T' masks the recessive 't'. Homozygous dominant plants (TT) are also tall, but differ genotypically from heterozygous plants. The recessive phenotype only appears in homozygous recessive individuals (tt).
Step-by-step explanation:
A pea plant with a genotype of Tt should be referred to as heterozygous. This means that it has two different alleles for the given trait, one dominant (T) and one recessive (t). In the case of pea plants, T is the allele for tallness, which is dominant over the allele for dwarfism (t). The phenotype of a heterozygous (Tt) pea plant is tall because the dominant allele 'T' masks the presence of the recessive allele 't'. It is important to note that while both homozygous dominant (TT) and heterozygous (Tt) pea plants are phenotypically tall, they differ at the genotypic level. Homozygous dominant plants have two copies of the dominant allele (TT), while heterozygous plants have one dominant and one recessive allele (Tt).
Phenotype expression depends on the inheritance of alleles. If a plant is homozygous recessive (tt), it will exhibit the recessive trait, which in the case of pea plant height, would be dwarfism. Mendel's laws of inheritance explain how these traits are passed on and expressed in offspring, with a typical 3:1 ratio of dominant to recessive traits in the progeny of two heterozygous parents.