The region of the chromosome with very few functional genes is called heterochromatin.
Heterochromatin generally refers to the gene-poor, densely packed, and repetitive sequence of DNA found in the centromere and telomere regions of eukaryotic chromosomes.
Heterochromatin is as opposed to euchromatin. The latter is a lightly packed and gene-rich sequence of DNA on chromosomes.
The densely packed feature of heterochromatin means that protein factors have no access to the region. Thus, they are thought to function in the regulation of genes as well as protect the integrity of chromosomes.
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