What is W chromatin?
In many species of butterflies and moths (Order: Lepidoptera), sex chromosome constitution is ZW in females and ZZ in males. Intriguingly, W chromosome is condensed and conspicuous in each cell nucleus during interphase. This is called W chromatin or sex chromatin. Hence, sex diagnosis is available by a relatively simple method (compared to conventional karyotyping) even in the very young stages when it is almost impossible to distinguish male and female morphologically. For details, please refer to Traut and Marec (1996).
Preparation
- Insects
- PBS buffer (or Ringer solution)
- Fixative (methanol: acetic acid = 3:1) [the fixative MUST be prepared every time]
- Stain (lactic acetic orcein solution) [should be prepared beforehand*]
*To make lactic acetic orcein: Condensed solution: 5 g of Orcein + 100 ml of lactic acid + 100 ml of acetic acid -> Keep it for more than 2 weeks (mix occasionally). -> Add equal volume of 50% acetic acid to the condensed solution.Procedures
- Dissection of insects Open fresh insects in PBS using fine forceps. Pick out Malpighian tubules and remove extra PBS.
- Fixation Put the Malpighian tubules in the fixative (10-30 sec) and then on a glass slide.
- Staining When most of the extra fixative evaporate (but should not be dried up), add 2 or 3 drops of lactic acetic orcein solution (use supernatant).
- Observation After 3 min, place a cover slip over the material and observe under a light microscope.
- Traut W and Marec F (1996) Sex chromatin in Lepidoptera. The Quarterly Review of Biology 71: 239-256.
