What is a three point test cross?
The three point test cross is the method of choice in determining linkage in organisms with many genetic markers. The principle of independent assortment assumes that different genes followed in patterns of inheritance analysis are on different chromosomes. Mendel studied seven traits in peas: each trait is now known to be located on separate chromosomes. (Mendel’s work was rediscovered by Bateson when his research gave progeny ratios that Bateson could not interpret. While Mendel’s work confirmed independent assortment ratios, it was the work of Morgan that finally provided an explanation for deviation from dihybrid ratios.) Independent assortment predicts that the percentage of parental gamete types will be equal to the percentage of recombinant gamete types. That is, if the parental cross is: AABB x aabb, the parental gamete types are: AB and ab. The recombinant types, produced through independent assortment, are Ab and aB. Thus, with independent assortment, the percentage of AB and
