In hackberry Celtis occidental the seed inside the fruit can

In hackberry (Celtis occidental), the seed inside the fruit can be either globular or ovoid. A cross between certain true-breeding lines of hackberry trees with globular seeds yielded a uniform F1 generation with globular seed. When two of the F1 trees are crossed, the resulting F2 generation has a ratio of 15 globular: 1 ovoid seeded trees. What pattern of inheritance is in agreement with these phenotypic ratios?

Solution

The pattern of inheritance is Epistasis, here Duplicate dominant genes (15:1):

In this given scenario, globular (G/g) and ovoid (O/o)

F1=GgOo

F2= GgOo x GgOo

GO=globular

Go=globular

gO=globular

go=ovoid

Complete dominance at both gene pairs, but either gene when dominant, epistatic to the other.

If a dominant allele of both gene loci produces the same phenotype without cumulative effect, i.e., independently the ratio will be 15:1.