What Mendel did according to the illustration would be called test-crossing.
Test-crossing
In genetics, test crossing is a procedure through which the zygosity of an individual can be determined - whether it is homzygous or heterozygous.
Test crossing requires that an organism who displays a dominant trait but whose zygosity is unknown is crossed with another organism of the same species but who displays the recessive version of the same trait.
By so doing and using the knowledge of probability, the resulting offspring from the cross will be used to determine the zygosity level of the parent.
More on test crossing can be found here: https://brainly.com/question/16805498
