After salivary gland cells from Drosophila are isolated and cultured in the presence of...

After salivary gland cells from Drosophila are isolated and cultured in the presence of radioactive thymidylic acid, auto-radiography is performed, revealing polytene chromosomes. Predict the distribution of the grains along the chromosomes.

HINT: This problem involves an understanding of the organization of DNA in polytene chromosomes. The key to its solution is to be aware that as a molecular tracer, will only be incorporated into DNA during its replication.