Wing flapping: this technique involves lifting one wing of a fly about 90 degrees so its wing membrane is horizontal and nearly touching the coverslip and using a pair of forceps to grab and hold the tip. After the wing has been lifted, the fly is rolled over on its side so that the wing membrane of the raised wing is facing down. The tip is then cut with another pair of forceps, after which the tip of the wing can be pulled away in a horizontal plane. This method has traditionally been the one recommended for obtaining polytene chromosome preparations from drosophilids. The advantages of this technique include:
- it is much easier to remove one whole wing than to cut the thorax in half for squash preparation.
- only a small amount of soft tissue remains attached to the chromosomes making them easier to spread and stain.
The major disadvantages of wing flipping include:
- the risk of contaminating the preparation with hemolymph from the cut wing, which can interfere with chromosome spreading and staining.
- the potential for displacing polytene nuclei during dissection of the wing, which can make subsequent identification difficult.