Polytene chromosomes
iGen3 16-01
Polytene chromosomes in Drosophila (2n = 4)

   Polytene chromosomes are produced by endoreplication, in which chromosomal DNA undergoes mitotic replication, but the strands do not separate. Ten rounds of endoreplication produces 210 = 1,024 DNA strands, which when arranged alongside of each other produce distinctive banding patterns. Endoreplication occurs in cells of the larval salivary glands of many Dipteran species, and increases production of mRNA for Glue Protein that the larvae use to anchor themselves to the walls of (for example) culture vials.

Figure 2002 by Griffiths et al.; All text material 2013 by Steven M. Carr