Genetic Linkage

Creighton and McClintock's Proof of Chromosomal Exchange During Crossing Over

They used corn chromosome 9 markers:

They created a heterozygote with the following characteristics:

They performed a testcross to this stock and analyzed the results.

If crossing over involves exchange of chromosomal material each recombinant chromosome would have on of the cytological landmarks. This is the result they obtained.  See the figure below.