An entomologist conducts crosses between swallowtail butterflies with different colored wings and observes the following results:
A cross between a butterfly with blue wings and a butterfly with white wings produces all offspring with light blue wings.
An F1 intercross between the light blue offspring produces offspring in the following ratio: 1 blue: 2 light blue: 1 white.
With further investigation, you discover that there are 2 alleles for this gene: one allele produces blue pigment, and the other allele produces a white pigment. Heterozygous butterflies express both the blue and the white pigment in equal amounts.
Assuming wing color in swallowtail butterflies is due to only one gene, what is the BEST description for the inheritance pattern observed at the molecular level for this character?