Introns may more freely accumulate point substitutions and other changes due to no selection pressure.  Introns evolve or accumulate mutations/changes much more rapidly than exons

#Id: 420

#Unit 2. Cellular Organization

Mammalian H2ABbd variant is excluded from the inactive X and forms a less stable nucleosome than canonical H2A

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#Unit 2. Cellular Organization

#Id: 422

#Unit 2. Cellular Organization

#Id: 423

#Unit 2. Cellular Organization

The second level of organization is the coiling of the 10-nm fiber of nucleosomes into a helical array to constitute the fiber of diameter 30 nm.

#Id: 424

#Unit 2. Cellular Organization

30 nm compacts the DNA 40-fold. This structure of this fiber requires the histone tails and is stabilized by linker histones.

#Id: 425

#Unit 2. Cellular Organization

This 30-nm fiber is further folded, results in 1000-fold compaction in euchromatin in interphase chromatin and in mitotic chromosomes to achieve an overall 10,000- fold compaction in euchromatin.