TT

Tt is most commonly encountered as a genetic notation used to describe a heterozygous genotype at a single gene locus. In this usage, the letter T represents a dominant allele and the letter t represents a recessive allele. An individual with the genotype Tt carries one copy of each allele, so the phenotype typically reflects the dominant trait, assuming complete dominance.

In Mendelian genetics, Tt is part of a simple dominant-recessive pattern. For a trait governed by a single gene with alleles T and t, crossing two heterozygotes Tt x Tt yields offspring with a genotype distribution of TT (25%), Tt (50%), and tt (25%). Phenotypes occur in a 3:1 ratio, with the dominant trait expressed in both TT and Tt individuals, and the recessive trait expressed only in tt individuals. This framework helps explain how variation in genotype corresponds to differences in phenotype within populations, and it is commonly used in introductory genetics to illustrate inheritance patterns and Hardy-Weinberg expectations.

Outside genetics, the two-letter combination Tt has no single standardized meaning and is rarely used as a formal symbol. The uppercase acronym TT is more common in other domains, denoting terms such as table tennis or Tourist Trophy. When encountered as Tt, it is typically a segment of a larger label or a shorthand in a specific study, rather than a distinct, widely recognized concept. See also TT for related abbreviations and genetic notation TT, Tt, and tt.