P

Fi plants with ^ plants with white kernels purple kernels plants with red kernels

1/16 plants with purple kernels 4/16 plants with dark-red kernels F2 6/16 plants with red kernels

4/16 plants with light-red kernels 1/16 plants with white kernels

Nilsson-Ehle interpreted this phenotypic ratio as the result of segregation of alleles at two loci. (Although he found alleles at three loci that affected kernel color, the two varieties used in this cross differed only at two of the loci.) He proposed that there were two alleles at each locus: one that produced red pigment and another that produced no pigment. We'll designate the alleles that encoded pigment A+ and B+ and the alleles that encoded no pigment and B~. Nilsson-Ehle recognized that the effects of the genes were additive. Each gene seemed to contribute equally to color; so the overall phenotype could be determined by adding the effects of all the genes, as shown in this table.

Genotype

Doses of pigment

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