Question

When the same chromosome is compared between two different cells, regions of heterochromatin and euchromatin are found in different locations between the two cells. Why does the state of chromatin packaging differ along the length of the same chromosome in two different cells?

Answer 1

Heterochromatin is the more condensed parts of a chromosome. They stain darker and the DNA is more compactly packed in this region. Euchromatin is the less condensed part of a chromosome. They stain lighter and the DNA is loosely packed in this region. The DNA of the euchromatin is actively transcribing and translating, while the DNA of the heterochromatin is not. This is the reason it is loosely packed at the euchromatin regions so the various enzymes could act on them. All the cells in the body constitute the same chromosomes. But the cells differ in their functions. The neurons may work differently than the gametes and the muscle cells may have different functions than the liver cells. The genes expressing at a time in the muscle cells would be different than the genes in the liver cells. The liver cells might never need the same products as a muscle cell does. So the same chromosome, which contains many different segments in form of genes might have different regions acting as euchromatin or heterochromatin for them.