Lack of Dominance

The conflict was that there were three distinct leaf color phenotypes among the selfed progeny. Some had dark green leaves, some had pale green and some had yellow. The plants with yellow leaves were much smaller and many were dying at two weeks of age. How can the pale green plant produce three phenotypes from selfing? Lack of dominance would explain this result. If the two alleles at this leaf color gene pair had a lack of dominance, we could propose the following: First, Y1 is the version of the leaf color gene that controls green color. Plants need two copies of this gene per cell in order to maximize this green color trait. The alternative allele at this gene pair, Y2 , is not recessive to the Y1 allele because we can distinguish between plants that are Y1 Y1 (dark green) from those that are Y1 Y2 (pale green). Selfing a pale green gives Y1 Y1 ; Y1Y2 ; Y2Y2 progeny as follows:

Thus the green progeny (Y1Y1) and yellow progeny (Y2Y2) would be expected to each be about ¼ of the progeny and the pale green would be ½. The frequencies of the leaf color phenotypes obtained in the selfed progeny would be a good test of the hypothesis of lack of dominance. Unfortunately, research is not always as easy as it looks on paper.