Soybean Experiment and Working Hypothesis

Two parents were identified in the field that differed by two traits. One parent had a pale green leaf color and three leaflets per leaf while the other parent had a dark green color and seven leaflets per leaf. Dr. Specht made crosses between the two parents and seven hybrid seeds were produced. He planted these seeds in the field and the following results were obtained.


What genetic hypotheses could you pose to explain the results obtained so far? These results can be a little confusing. One way to make the information simpler is to look at one trait at a time.

1) Leaf number trait: the three x seven cross gave all progeny with three leaflets

2) Leaf color trait: the pale x dark cross gave about ½ pale + ½ dark offspring

How could we explain these results? The leaflet number trait is easiest to explain. Both parents could be homozygous and the three leaflet trait completely dominant to the seven leaflet trait. Their offspring are heterozygous but express the dominant three leaflet phenotype. Genotypes for this cross could be as follows:

Now let’s take a look at the leaf color trait, which is a bit more complicated. The results obtained for the leaf color traits could be explained in two ways. All explanations require one parent to be heterozygous.

The Yy genotype could represent the pale green phenotype and yy dark green, or just as likely, Yy dark green and yy pale green. Either way gives the same resulting progeny from this cross. Therefore additional experimental evidence must be obtained. What would be the easiest experiment to perform that would test the proposed hypotheses?