Final answer:
To visualize Drosophila polytene chromosomes, scientists use Giemsa stain, which allows for the observation of banding patterns without fluorescence. This stain assists in the routine identification and characterization of chromosomes using bright-field microscopy.
Step-by-step explanation:
To visualize Drosophila polytene chromosomes, which are found in the salivary glands of fruit flies, scientists often use a non-fluorescent DNA stain. A popular choice for staining chromosomes to see the banding patterns clearly under a microscope is Giemsa stain. This traditional staining method allows for the identification of tightly coiled DNA and the proteins that make up the chromosomes. When using bright-field microscopy following the Giemsa staining, one can observe approximately 400-800 bands, aiding in the identification and characterization of each chromosome pair, along with their size and centromere location.
Geneticists pursue a routine identification process by capturing digital images of the stained chromosomes and manually arranging them to depict a karyotype. This classic depiction aligns homologous chromosome pairs in numerical order from longest to shortest, thus providing a comprehensive visual of the chromosome structure and arrangement. Although fluorescent dyes like ethidium bromide and SYBR green are commonly used for DNA visualization, they require UV light for excitation and are not suitable for Giemsa stain procedures aiming for non-fluorescent visualization.