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.