Essential Genetics 6th Edition by Daniel Hartl

Exercise 1

In Drosophila, the dominant allele Cy (Curly) results in curly wings. The cross Cy/1 3 Cy/1, where 1 represents the wildtype allele of Cy, results in a ratio of 2 curly : 1 wildtype among the progeny. When the curly progeny in this generation are crossed with one another, their offspring also show a ratio of 2 curly : 1 wildtype. How can this result be explained?