iGenetics 3rd Edition by Peter Russell

Exercise 5

In Drosophila , the vestigial ( vg ) gene is located on chromosome 2. Homozygous vg / vg flies have incompletely formed vestigial wings; vg + /- flies have wild-type long wings. A new eye mutation called maroonlike ( mal ) is isolated. Homozygous mal / mal flies have maroon-colored eyes; mal + / - flies have wild-type red eyes. The location of the mal gene is unknown, and you are asked to design an experiment to determine whether it is on chromosome 2.
You cross maroon-eyed females to vestigial males and obtain all wild-type F 1 progeny. Then you allow the F 1 offspring to interbreed. As soon as the F₂ offspring start to hatch, you begin to classify the flies. Among the first six newly hatched flies, you find four wild type, one vestigial- winged, red-eyed fly, and one vestigial-winged, maroon-eyed fly. You immediately conclude that: (1) mal is not X linked; and (2) mal is not linked to vg. How could you tell on the basis of this small sample? On what chromosomes might mal be located? ( Hint : There is no crossing-over in male Drosophila flies.)