History of test cross
Test crossings were first employed in Gregor Mendel's plant hybridization research. He demonstrates that the "signification" (today called zygosity) of an individual for a dominant characteristic is decided by the expression patterns of the subsequent generation when researching the inheritance of dominant and recessive traits in pea plants.
The ideas of test crosses were widely used in experiments when Mendel's work was rediscovered in the early 1900s. Thomas Hunt Morgan carried out test crossings between 1908 and 1911 to ascertain the mode of inheritance of a white eye-color mutation in Drosophila. These test cross-studies were fundamental to the identification of sex-related characteristics.
Design of a test cross
The following test-crosses between individuals with the recessive parent and pure dominant (A) or hybrid dominant (B) individuals show
- The condition clearly shows that when an organism has a homozygous dominant genotype, all of its progeny from test crosses will exhibit the dominant phenotype.
- If the organism's genotype is heterozygous, then half of the test cross's offspring will have a dominant trait, while the other half will have a recessive trait.
Define and design a test cross.
Finding the genotype of an organism that is demonstrating dominance for a specific attribute is the goal of a test-cross experiment.