To prepare salivary gland chromosomes in Drosophila melanogaster.
- Stereo zoom/Dissecting microscope
- Third instar larva
- 1N HCl
- Physiological saline (0.7% NaCl)
- Lacto aceto orcein
- 45% acetic acid
- Nail polish or wax for sealing
- Slides and cover slips
- Dissect the salivary gland of the third instar in physiological saline.
- Place it in 1N HCl for 2–3 min.
- Transfer it to 2% Lacto Aceto orcein stain for 30 min.
- Squash it with freshly prepared 45% acetic acid.
- Seal the edges of cover slips with nail polish or wax.
- Observe under the microscope for polytene chromosome.
- Edouard-Gérard Balbiani, in 1881, observed salivary gland chromosomes
in Chironomous larva.
- Theophilus Painter discovered the same in Drosophila melanogaster.
- The polytene chromosomes are the largest chromosomes available for
- These chromosomes are clearly seen in the third instar larva of Drosophila
- The salivary gland chromosomes undergo somatic pairing and endoduplication
- This multistranded chromosome contains 1024 chromosomal fibrils.
- When stained, chromonema shows bands and interbands.
- Along the length, there are bulged regions called Balbiani rings, or puffs,
which are the sites of genetic action.
- Thus, this chromosome has a common chromocenter, with 5 long areas