In Drosophila, vestigial wing (vg), hairy body (h), and eyeless (ey) are recessive mutations on chromosomes 2, 3, and 4, respectively. Wild-type males that had been irradiated with X rays were crossed to triply homozygous recessive females. The F1 males (all phenotypically wildtype) were then testcrossed to triply homozygous recessive females. Most of the F₁ males produced eight classes of progeny in approximately equal proportions, as would be expected if the vg, h, and ey genes assort independently. However, one F₁ male produced only four classes of offspring, each approximately one-fourth of the total: (1) wild-type, (2) eyeless, (3) vestigial, hairy, and (4) vestigial, hairy, eyeless. What kind of chromosome aberration did the exceptional F₁ male carry, and which chromosomes were involved?