Study of Polytene Chromosomes from Drosophila Larva

 

Practical No. 2

Study of Polytene Chromosomes from Drosophila Larva

Aim

To prepare and study polytene chromosomes from the salivary glands of Drosophila larva.

Requirements

1. Third instar Drosophila larvae
2. Compound microscope
3. Glass slides and cover slips
4. Fine needles and forceps
5. Aceto-orcein or aceto-carmine stain
6. Watch glass
7. Blotting paper
8. Dissecting microscope

Principle

Polytene chromosomes in Drosophila larvae are giant chromosomes formed by repeated DNA replication without cytokinesis. They are present in salivary gland cells and exhibit characteristic banding patterns useful in genetic and cytological studies.

Procedure

1. Select a healthy third instar Drosophila larva.
2. Place the larva on a clean slide containing a drop of stain.
3. Hold the mouth hooks with forceps and gently pull the posterior end.
4. The salivary glands appear as paired transparent sacs attached near the head region.
5. Transfer the glands to a fresh drop of stain.
6. Stain for about 5 minutes.
7. Place a cover slip carefully over the material.
8. Gently squash the glands using blotting paper.
9. Observe under the microscope.

Observation

Distinct giant polytene chromosomes with alternating dark and light bands are visible. The chromosomes may radiate from a common chromocenter.

Result

Polytene chromosomes from salivary gland cells of Drosophila larva were successfully prepared and observed.

Precautions

1. Use only third instar larvae for best results.
2. Avoid over-squashing the glands.
3. Ensure proper staining before observation.
4. Handle salivary glands carefully to avoid damage.