Marcus Rhoades on preferential segregation in maize

Birchler, JA,  Genetics,  203:1489-1490. 2016.

Rhoades was studying a variant form of chromosome 10 with a conspicuous abnormality; it carried extensive heterochromatin at the tip of the long arm. This variant had been found by Albert Longley in indigenous maize varieties from the southwestern United States and provided to Rhoades for the pedestrian task of determining the recombination frequency between the anthocyanin pigment gene, R, and the end of the chromosome. The abnormal chromosome 10 originally carried the recessive, r, allele (colorless kernels) and was crossed to other lines carrying the dominant R (red kernels). Much to the surprise of Rhoades, when these heterozygotes were testcrossed with the recessive, there was a strong skew from a 1:1 ratio. Rather than the roughly even mix of colorless and red kernels that he expected, around two-thirds were colorless. This excess of r alleles was caused by linkage to the variant chromosome; in the few progeny that transferred the dominant R allele to the abnormal chromosome 10, subsequent testcrosses demonstrated that it was now the dominant allele that was preferentially inherited.