In experiments published in 1918 that sought to verify and expand the genetic linkage and recombination theory proposed by Morgan, Thomas Bregger studied potential genetic linkage in corn (Zea mays) for genes controlling kernel color (colored is dominant to colorless) and starch content (starchy is dominant to waxy). Bregger performed two crosses. In Cross 1, pure-breeding colored, starchy-kernel plants (C1 Wx/C1 Wx) were crossed to plants pure-breeding for colorless, waxy kernels (c1 wx/c1 wx). The F₁ of this cross were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:
Phenotype Number
Colored, waxy 310
Colored, starchy 858
Colorless, waxy 781
Colorless, starchy 311
2260
In Cross 2, plants pure-breeding for colored, waxy kernels (C1 wx/C1 wx) and colorless, starchy kernels (c1 Wx/c1 Wx) were mated, and their F₁ were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:
Phenotype Number
Colored, waxy 340
Colored, starchy 115
Colorless, waxy 92
Colorless, starchy 298
845
Calculate the recombination frequency for each of the progeny groups.
4. Genetic Mapping and Linkage
Crossing Over and Recombinants