The punnett square is a resource that was conceived by RC Punnett, a collaborative geneticist for William Batenson (both lived between the end of the 19th century and the beginning of the 20th century, actively participating in the rediscovery of Mendel's work), which greatly facilitates the making of crosses between F-1 heterozygotes, by filling in the boxes that compose it with the genotypes resulting from the crossing performed.
The Punnet square of two organisms where one has the Tt genotype and the other the Tt genotype is shown in the image below:
