You discover a new mutation in Drosophila that causes an abnormal wing shape. When a male fly with this mutation is crossed to a homozygous normal female, the F1 are all wild-type phenotypically. The F2 flies consist of 1/2 phenotypically normal females, 1/4 phenotypically normal males, and 1/4 males with abnormal wings. What is the MOST likely explanation for the new mutant allele?