Some cells at particular stages contain large
nuclei with giant or large sized chromosomes. The giant chromosomes are the Polytene and Lamp brush chromosomes.
Polytene Chromosome (Salivary Gland Chromosomes)

An Italian cytologist E. G. Balbiani (1881)
has observed peculiar structures in the nuclei of salivary glands of Chironomous. Later, T.
Painter and co-workers observed the same type of structures in the salivary
gland of Drosophila and
recognized them as chromosomes. These chromosomes are characterized by big size
swelling and cross striations.Because they were observed first in salivary
glands they were called salivary
gland chromosomes.
Maternal and paternal homologous
chromosomes remain associated side by side in polytene chromosome. This phenomenon
is called somatic pairing.ThusDrosophila has
only four polytene chromosomes.
Chromosome puffs or Balbiani Rings
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Chromosome Puffs |